Haha, two months late to the party but yes, the DOS executable of Redguard has both software and 3dfx versions. Not sure if they are included in the GOG version, as they require a slightly different installation.

I bought this version of the game expecting it to be unplayable, but I ran it perfect without any problems. I played for about a hour because I didn't have any more time.

I haven't updated this specific PC to Windows 10, but it's a pretty powerful computer with Windows 7.

Yeah, runs pretty bad for me as well. I don't consider 10-15fps all that playable.

There should be a software version, but it looks like it doesn't work, so we are stuck playing it in 3dfx mode? Couldn't they add the software verson too? Chances are it would run better.

From the Redguard folder, I ran "DOSBox Configuration" and changed some of the settings. From overlay, I want to OpenGL, and I also chose a scaler.

I drop zero frames with overlay, but the game runs more smoothly with OpenGL enabled in the configuration utility.

With the GOG version of DB, I can't seem to disable GLIDE. When I force disable it, the game does not boot up at all. I hope that helps some.

The friendly support of GOG refunded me the game after I told them about the serious performance-problems. That's why I like GOG.
But to the problem: It does indeed run terribly slow - I own the game from years back, and it was a wonderfully fluent experience back then on my Voodoo 2. So please don't say the game was always that slow as it is here, it's not true. Changing the cylces doesn't help anything - but that's normal, as the game is already running on maximal cycles (or am I wrong here? I can't remember exactly), you can't overclock Dosbox. I think that's the only problem with this game: The Dosbox is absolutely unable to give this game proper speed. The limitation of the emulator itself is the problem, not the cpu-power of your computer. I've installed the game again from my own discs just to try the software mode to have a comparison - it's nearly the same performance as with emulated 3dfx.
Sure, there are some folks who think 15-20 fps isn't too bad - for me it's just masochism.
If GOG manages to make the game playable, I'll consider to rebuy it, as it's a great game.

This is not a glide wrapper (nGlide) problem, DosBox runs with dynamic core (JIT) at max.
The only solution I see (if possible) would be to change the way DosBox emulates glide.
I bet that those who wrote Glide emulation for DB knew what they were doing, so I'm not very optimistic.
I've no idea what DosBox does, but it probably passes glide calls from emulated DOS to glide wrapper dll.
Maybe some calls could be buffered, no idea.
Note that (at least glide2x) had no batching, each primitive required 1 (or more in the case of state changes) glide calls.
(note that back then glide API was actually superior to early D3D from what I remember and ran smoothly).

I've noticed that performance depends on amount of geometry drawn (=glide draw calls) so my guess is that
it's indeed a problem with how DosBox passes glide calls, I think DosBox itself has no problem emulating the CPU.

Wouldn't want to get anyone too excited, but I will say that I ran nglide_config.exe in the DOSBOX directory and made 2 changes, and now the game runs much better. The things I changed were Screen Resolution to By app (Default), Vertical Synchronization to Off. I'm curious if someone else has any luck with that. Indoor areas run especially well.

Almost forgot, I changed the graphics mode to OpenGL from the DOSBox configuration shortcut.

I'm not a tech person, so I don't really know what I'm doing other than guesswork. Seems to have done something, though.

I need to correct my previous statement a bit.
I tried to replace glide2x.ovl with a custom one that does not send anything to glide wrapper.
Framerate hasn't improved a bit => this means it's fully CPU bound and DosBox cannot emulate RedGuard fast enough.
So wrapping calls to glide wrapper is not the problem.
I'm afraid nothing can be done to improve performance...

You might be amazed at what a processor upgrade can do.

Is that so? Please show me a fluently working version of Redguard on dosbox, I can't imagine what beast of a pc I should have to play Redguard then. Dosbox is limited, that's the only problem here in my opinion. And as k_mar says, it isn't a problem of glide emulation, software mode isn't better.

It's probably a matter of expectation and perception. I run GOG-Redguard on an old XP laptop with an Intel graphics card, and I'm happy with the performance (after applying applied a few conf-tweaks - but nothing that hasn't been described elsewhere thousands of times). Movement is fluent, no stuttering, speed comparable to that of Morrowind with a character having a speed of about 50.
If you were playing Redguard on my laptop, you might find it slow, for example if you are used to running from one end of town to the other in a few seconds (in other computer games).

PS: I have also been playing Reguard on a much more powerful Win10 desktop. Slightly faster, but not much. Seems Redguard and / or DosBox can't make use of multi-core CPU's and a lot of RAM (no surprise) - and running single-core, modern CPU's are not that fast.

If it hasn't already been mentioned, iirc GOG didn't include the software (non-Glide) version because it has a game-breaking bug, making the game unwinnable.