Its fine if you don't care about comfort, but going with too high of a spring rate on a road-use car is a safety issue, not just a comfort one. I wouldn't go much past 400#, personally. Remember, its the handling balance that you want, not the hairy-edge limits (especially for autocross), and higher spring rates don't make you any more of a man h:

Another thing to keep in mind is the f/r spring ratio. Its popular (read: cool, trendy, accepted) to get a higher number in the rear, but that really all depends on your driving style. Most, if not ALL of the aftermarket springs & coilovers out there have a higher rate in the front and handle just fine. If you are a fast-in, hamfisted sort of driver, the higher rear bias will just make you oversteer and scrub off a lot of speed, or just spin (I spun my car a lot in my first and second season). If you're a very controlled, slow-in, fast-out sorta driver, then the higher rear rate is fine. BUT if you choose a higher rear bias, NEVER drive at 10/10 (or even 8.5/10) on public roads. There are too many uncontrollable variables to be safe. :edit: Really, this applies to anybody in any car. I've come too close to disaster... keep it on the track h: