I don't know how they are getting away with stock bottom ends, with 300+ hp, But I have seen a stock bottom end take all of the rods and turn them into an "S"! No joke on the dyno this motor hit 315hp and bent em all!!!
If you are looking at running big nitrous hp don't cheap out on your motor it's a pay me now or pay me later game your going to be playing! It's just way cheaper to do the pay me now, rather than when you see big chunks of your pistons and your rods blow out of your motor! Nitrous is the cheapest easiest HP you can get, and that's the great part of this stuff. Just don't cheap out on your motor, it will cost you more in the long run!!!