I think Denny posted a good link a while back on SCR, DCR, and practical limits for pump gas... I think 8.5:1 DCR is nominal tops for pump premium but some factors can push that up like high altitude, aluminum heads, etc... mine is at 8.9:1 (10.8:1 SCR) and will run on 91 octane but I have to take out a bunch of timing (32-33* total) to do it... On 100 octane unleaded I run 38-39* and it screams.

-Chris