The 8.5 will be just fine, most people that run anything more can't drive it anyway. I run an 8.5 in one of mine and I have way more than enough power everywhere I have run.
If you want to save a little check out the SMC 8.5 at
www.smc-racing.net
They are $50 and I see no difference on track between my Gen2 8.5 and the smc. The smc is 1/2 the price.