I'll be using the fixed logic loop at 200FPSish and then spitting out a frame, and if the card has got Vsync on, the next frame won't come round until whatever the monitors refresh rate is (60-100Hz ish). If they have Vsync off, the game will run at a Max of 200HZ, but obviously rendering when it feels like, up to 200Hz. So will this whole lag thing still be an issue?
Yes. Anything that has a lot of fillrate going on and very few polys. Ie... Blitzmax... unfortunately!