If you run low boost you can run regular pump gas w/a engine of having 8.5:1.
You could go to 9.0:1 also with low boost & conservative timing on regular pump gas.
The advantages to aftermarket pistons over NOS forged TRW 307 pistons? Normally, they will be lighter, if designed correctly, larger/better quench area = less chance of detonation. Better ring package. So, a better designed aftermarket piston should give you more power, it is not going to be a day & night difference in power.
Just make sure you get close to a zero deck height.
If you go too low on the compression, mileage suffers, turbo response is slower, (slower to get into boost).
If you just limit your boost to say approx 10 - 12 PSI I would run closer to 9.0:1 & run premium pump gas.
