10.5 or 12.5?Also what would be the biggest shot of nitrous i could use with either one of those?Also how much horsepower would 10.5 pistons add and how much would 12.5 add?

Do a search there info floating around on this. You get about 4% for every compression point raised. If you have the ability to retard timing and adjust fuel, 12.5:1 will make you more power. As far as nitrous, you will need to pull both timing and add fuel when you start spraying on 12.5:1. If you are comfortable tuning and understand that everything requires time to get it right, the 12.5:1 will give you about 8% more power than the 10.5:1.



15.9 @ 86.7mph

Smooth idle? We don't need no stinking smooth idle.

Mods List:
http://highlander.dsmpower.com/sig.htm

I just went with the 10.5:1 and it feels great! A good middle of the road CR is the 11.5:1 I think they need to be special ordered, but they are out there.

I chose the 10.5s because I know that some day down the road I will decide I've gone as far as I want to with the NA setup and will want boost or to spray. With the 10.5 it would take less effort to tune those compared to anything higher. After a couple years of higher compression I'll have gained a lot of insight into proper tuning and maybe be able to handle a turbo system at that time.

Use the search utility and you'll find enough info to make your head spin! :P