I have 3.69 gears as I said below making close to 750whp and I wish they were taller. I've considered the 3.35 diff and even the 3.13. I think the 3.69's are perfect up to about 600whp. I like the 4.08's up to about 450-500whp. It's just personal preference but I do worry at some point you would be lugging a turbo car everywhere with too tall of a diff. It seems to just depend on what you like when driving in terms of feel and how much power you're making.