Just checked out the performance of NOLF and SHOGO on 2 of my machines: Win98 Xeon 3230 w/ Radeon 9800 Pro & Win XP Xeon 5690 w/GTX 780ti.
Both games run smooth at over 60FPS with no stuttering no matter what is going on onscreen. I did notice that some minor frame dropping on the XP machine particularly while turning and strafing at the same time but I'm betting this is mostly due to the mouse or possibly newer drivers. I use to have a P4 3.4Ghz with the Radeon 9800 Pro and I don't remember there being any frame rate problems with that either...
I also played it on the Xeon 3230 Win98 machine with a single Voodoo 2 card. This generally ran the game at 60FPS but I did see when there were a lot of particle effects (explosions, smoke, etc...) that it did slow down to around 30 FPS or so. This is just eyeballing everything but I thought I'd chime in.
Just gave these a try on my Shuttle PC: Athlon 3700+ W/Geforce ti4200 Win XP, Everything ran perfectly and over 60 FPS at all times on both NOLF and SHOGO.