They are too close to pick one. So they´ll be winning and loosing against each other with different games, how much depends on what the specific game craves.
So I´d say, try the other one and see if it "convinces" you more than your current one for your current usage. You may or may not perceive any difference.

 
 
The GTX 550 Ti is a better beast. It offers good performances, more compatibility and requires less power. Its <span class="bold">die</span> is also larger, which means more surface contact with the heatsink and a better cooling efficiency.


Take a look at <span class="bold">Hardware Compare</span> for a complete comparison of the two GPU's.



Maximum Thermal Design Power (Power Consumption)


 ▪  GeForce GTX 550 Ti:  116 Watts  (TDP)
 ▪  Radeon HD 4870 1GB:  150 Watts  (TDP)



Theoretical Benchmarks


Memory Bandwidth:  Theoretically, the Radeon HD 4870 1GB should perform just a bit faster than the GeForce GTX 550 Ti overall. (17% faster)

Texel Rate:  The Radeon HD 4870 1GB will be a little bit (approximately 4%) better at anisotropic filtering than the GeForce GTX 550 Ti.

Pixel Rate:  The GeForce GTX 550 Ti will be much (approximately 80%) faster with regards to AA than the Radeon HD 4870 1GB, and should be able to handle higher resolutions more effectively.



Hardware Compatibility


▪  GeForce GTX 550 Ti:  DirectX 11  /  OpenGL 4.1
▪  Radeon HD 4870 1GB:  DirectX 10.1  /  OpenGL 3.0

This PC i am using for surfing has a 550 Ti...(the one for gaming has a Radeon).
That said.....best way is to test them. Because you didn't told us about the Memory (the Radeon was sold with 512 MB or
1 GB, the Ti 1 - 3 GB).
For me it was a compromise between money (GTX650 TI) and performance.
No problem running games like Grid 2 with it....only downside: she is noisy (one of the reasons i don't use this PC for gaming).

To the best of my knowledge the HD is only in 1GB. At any rate I suppose I will test them both. The last card I bought myself was an all in wonder if that tells you how long it's been.

Your post is like a bad advertisement, written for people who don't know very much. 30W difference in power in a full size desktop PC is a completely irrelevant delta, I thought it was more! It's well withing the "who cares" category on a desktop PC. Cooling, on the other hand, depends on the manufacturer, not the die size. That`s just voodoo.

DX11 is completely irrelevant for either card, is DX11 ever a requirement for a game that runs on these cards? I can't name a single one. Every game that requires DX11 is made for a way beefier card than these peanuts.

Finally, all theoretical benchmarks are such bullshit. Just test the card. Reading some tech voodoo from fanbois will get you nowhere, fast.

Tech voodoo. Can't die soon enough.

Reminds me of the theoretical output of the PS2 through it's graphics alone, something like 6 GigaFlops; It uses Jargon we can't really relate to. What's a flop? What's a Teraflop? Why does it matter? It's not something i can measure or use so i have nothing to compare against.

Quite often it's hacks or interesting approaches to using the limitations that ends up with even better looks and performance than raw power.

Then there's DX11... Can't think of any examples either, i know Morrowind used DX9, and PCSX2 has DX9/11 modes, but i can't think of anything that DX10-DX12 really bring to the table that i would require them to work with it for. Maybe some of the newer visual features/filters/effects used in Arkham Asylum... but that's a guess...

Based on this comparison at Anandtech Bench, the 550 looks to me like the better choice.

AMD announced its 300 series, which are DirectX 12 fully compatible. Nvidia will probably start shelling their versions in the fall.

AMD cards are cheaper, but definitely hoter. So they do require some serious ventilation. Nvidia are not that hot, they have lower consumption, but they are not as performant.

Generalisations tend to be wrong if you look at details. For the current generation NVIDIA managed to cut power down significantly, but next gen AMD is also taking this route, from the rumours I've seen. In the past there were times when NVIDIA cards were very power hungry.

I'd say that the best thing is to compare specific chips. In this case the NVIDIA chip clearly takes less power and performs around the same as the AMD one, so it's the way to go.

AMD will start to reduce power consumption and make their cards cooler starting with the 300 series. Pricing..well, will see tomorrow when AMD launches the RX390. But it will be probably lower than Titan or the Fiji XT. Looking forward to see if Nvidia will enter in a price war or will avoid that, just like they did the last years (though i doubt that they can keep the prices so high, seeing what the competition offers at half price).

And, true, Nvidia started making their cards cooler and with a lower power consumption starting with the 600 series, if i recall correctly.

This is probably a little of topic, but I have a GeForce GT 220 from Galaxy, and it was a good card back in the day, but now, in my rig the GPU fan spins up loud anytime I play a game (not every game), but like Amnesia, Dear Esther, Don't Starve, or some other 3D game (not new) my GPU fan turns up the rotations and noise... never had my PC shut down, from heat, but... it is loud, and my GPU does get hot in terms of what HW monitor says, sometimes during gameplay even with settings on low or medium my GPU still spins faster than normal, (which during gameplay I understand).

My GPU runs on idle or browsing internet or just sitting there at around 53 degrees Celsius, and during gameplay it goes up to about 75-80ish.

These are normal temperatures. No sure if they're normal for this particular card, but they're in the normal range for GPU's.

The first option you have is cleaning, and possibly oiling, the card's fan. A second option is to buy a new card and get additional performance. The 220 is a low end card, so it won't be too expensive to get something better.

True that! My GPU is old... I am saving up to build a new gaming rig. My current rig is a older AMD Sempron LE-1300 CPU (yeah don't laugh) so really upgrading this GPU won't do much when my CPU stinks as well lol!

Yeah, clean that card and when you have the money buy that new rig.

Upgrading the GPU could still allow you to game at higher resolutions at the same FPS, even if the CPU is the bottleneck.

In your case I'd say:

It's not a big deal to buy out of step. Doubly so if your new PC will be a low end one like the previous one, so the new GPU will fit your current PSU. That said, the BIOS might not be compatible with a newer GPU. That happens.

Also, you can buy a used CPU like this one or this one for around $10 on eBay, and you'll have dual cores and a little faster single threaded speed. You can find even faster ones for not a lot more. Again, good to make sure that the PSU can support it, and make sure the BIOS supports it (which is easier to find out than with GPU's). (Also, the Sempron's fan may not be good enough.)