Seriously.
Quit trying to cheap your way out. Spend the extra few dollars and put premium in, no matter what. Like Bio stated earlier, the manufacturer doesn't put octane ratings in the owners manual for sh1ts and giggles. There's even a sticker inside your gas cap saying "PREMIUM ONLY" - You should probably listen to that.
These car's are prone to KR. Especially stock, since the front manifolds breathe no better than a coffee straw. My car saw 7* KR completely stock on 93. You want to run 91 or 93 at all times to lower the amount of KR you have. Since it is your biggest enemy.
Here how about this, run 87, beat the sh1t out of it and tell us what happens later on.
A lot of us know what we are talking about and have been in the 3800 scene since it started well over a decade+ ago. Take out word for it, and run Premium. Quit trying to be cheap. If you want to run 87, get a N/A car.