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What are the ACTUAL system requirements? I watched a video where a guy was above minimum specs by a little bit, but set everything to low and got about 40 fps. I hear that it's "well optimized" but I wonder if that means optimized for over-spec PCs.

I'm a bit under spec, and I was hoping the optimized thing meant I wouldn't have to put it on the lowest settings to get a decent framerate. I don't mind dropping most things to low/medium, and lower-than-average resolution, and no fanciness (vsync, anti-alias, etc). But I don't want it to look terribly wrong and only get 20 fps.

Oh ok why don't I mention my specs:

AMD Athlon 750k Quad Core
Nvidia GTX 650
8 gigs of ram (of some type)

I get it, it's lower than minimum, but I never trust that. It's not like the intro screen will say "You literally can't run this, goodbye". I've played many games I'm below spec on that run pretty decent. That's what I'm at least hoping for here.
MadOverlord.755: I'm a bit under spec,

AMD Athlon 750k Quad Core
Nvidia GTX 650
8 gigs of ram (of some type)
** That's an epic understatement. The Witcher 3 is probably the most graphically intensive game out there at present, and all of the usual 'under spec' boundaries don't apply. Having said that, I run it on dual GTX-580s on 'high' and get acceptable (forced 30) frame rates. My i7 CPU is superior to yours, and I have twice as much RAM. Don't expect miracles on your system.
MadOverlord.755: Oh ok why don't I mention my specs:
You left out the most important detail, your resolution.

I'm always at a loss why people never include it.
My guess is you'll get around 20-30FPS depending on your resolution, likely closer to 30FPS if you choose lowest.

If you own Witcher 2 you could play that at let's say medium/high to make up for the increased IQ difference they added when they upgraded RED engine for Witcher 3 to get a feel of how it's going to run.

My advice: wait, it's definitely worth it. This game was made with many details and it's terrific to actually be able to see them.
Kleetus: You left out the most important detail, your resolution.

I'm always at a loss why people never include it.
I don't really know. My answer was "lower-than-average", which I guess you could take to mean 1024x760, or 800x600 if desperate, or whatever. I don't zero in on one resolution.
what about me

AMD- A4-5000 APU quad core with Radeon 8330 Graphics HD 1.50GHz

8.00 gb of ram with 7.44 usable

windows 8 64 bit processor

I can go up to 1080 but things run better at 720.

Im not a graphics whore, I just beat mgs5 on an xbox 360 and thought it looked terrific
jdawg4876: Radeon 8330
I wouldn't even bother trying.
I run it with all settings on high and 30 fps on 1680x1050.

AMD A8-5600K 3.6 Ghz
AMD Radeon HD 7850 1GB

My cheap quadcore gets the job done. The game doesn't seem too CPU-hungry. My GPU is roughly on the same level as a GTX 660, so your GTX 650 might do at low/medium settings. I recommend searching YouTube for videos where people play the game with the same components as you. They will usually have a framerate-counter in the video, and settings in the description.
GTX 770 and an i7 manages to hold a steady 60fps at HIGH settings, with Foliage Distance and Shadows set to MEDIUM. (1920x1080)

My GTX 970 - i7-4770k - 16GB RAM hold a steady 60fps with everything set to ULTRA @ 1080p, with Hairworks enabled.
The game really is super demanding - especially on the highest settings. I am using a 980TI and I still only get around 65 FPS with all features on (excluding hairworks) in 2560X1440. If I turn on hairworks the FPS drops down to high 40s / low 50s.
Well, an update. I got the game. I set most everything to off/low and 1024x768. The performance I get really varies. I'd say I typically get from 15-30 fps, depending on how much is on the screen. It's okay, the only problem is certain combats are nearly impossible to play. I'm totally happy with 30, and I can even tolerate lower to a fault.

I don't think I'm unhappy. I was going to get it at some point anyway. But, looking at my specs, I can't really recommend someone with a similar system getting it. Especially the kind of person that needs smoothness all the time.
MadOverlord.755: I'd say I typically get from 15-30 fps
Yeah, that's about what I was getting with a 650. Playable, but combat could get badly annoying. If you have it in your budget to upgrade, it's worth it.

The game looks so, so amazing at 4k with everything on max. It looks like its own sequel, compared to how it looked at pretty much minimum. I'm almost never a graphics snob (this is GOG after all, where there are games for sale from the 19890s), but I have to say, Witcher 3 is so atmospheric that it really benefits from the graphics boost.