how much depends on how you plan to put down that power..
by saying 250 to the wheel, you're either talking a pretty beefy flat-6, a V8, or something that's pretty custom. the general number is 300hp.. it's torque that kills the tranny though.. (like a v8).. if you don't do hard launches, the 901 should hold plenty of power, even beyond 300..
my car won't make anywhere near 300.. but even if it did, i'd never have to worry about the 901 because i'll never be making that much torque (VERY hard to build boost in 1st gear)..
Jeff - turbo 914 - in the middle of welding together my custom a-w intercooler..