All this framerate nonsense is funny. I never noticed any slowdown in KZ1, since I'm more of a casual gamer than anything. I never notice small issues like framerate or screen tearing. I find that some people put too much emphasis on it.
What I think matters more to casual gamers is the ability to join a game within seconds. Which MW2 is better at. I have played about 24 hours of KZ2 and 100 hours of MW2. I like the game play more in KZ2 but play MW2 a lot more since my FL is always playing it and I can join a game in about 20 seconds. No matter how much it lags..... Laggy POS.