It's a close match between the processor and gfx card.
But all that depends on just what the hell stuff you're running it on.
Lemme put it this way; I have a 1.4ghz tbird and a geforce2 ultra. At everything dialed all the way up (including the card, mind you), it will be right at 30fps when the action gets intense and there's 5 guys shooting shotguns/ar15's at you. Not enough to cause lag, but just enough to cause you to overshoot the mark when you're whirling around with the uzis in bullet-time.
Pair that 1.4ghz up with a Ti4600, and there is no doubt it would be silky smooth all the time. Pair that Ti4600 up with a 1ghz P3, and it will get choppy with more than 3 guys on screen.
Same deal with Deus Ex.
If you asked me what processor you need to handle the physics, I'd say a 1.2ghz tbird. As far as the video card, a Geforce3 will give you just a tiny bit of breathing room.