Hey i used arias 10.1:1 on my 81.5mm gsr and made 340whp @13 psi on 93, with a daily driver tune by "the king" john vega. 10:1 is better for a street car because of the simple fact that off boost you will have more throttle response and pickup. you won't be riding at 10+ boost all the time, so why not have some good power in the mean time. 8.5 is for high hp race cars(30psi). 9.1-9.5 is better, but if all you want is 340-380 whp, go with the higher comp. thats from my personal expirience.