Your stock GSR engine should be 10:1 already. You can go 11:1 or high 10.x:1 without any problems using a fairly conservative tune. You could go all the way to 11'5:1 if you really wanted, but you're really walking the fence for tuning safety, gas quality, and ambient air temp. There are too many variables for a daily driver to make me feel safe about that in all seasons and all conditions. People do compression ratios like that all the time on the street, but I think the safety margin is just too small on pump gas.