318 timing

Since I have had my car back we have been messing with the timing. It seems to get better everytime its advanced. right now its about 15 degrees. It runs great but I don't think it has reached its full potential. What does everyone think the timing should be set at.

Here are my mods: 1974 318 Duster
-Bored .30 over
-3 angle valve job with port and polish
-340 cam and lifters
-340 valve springs
-edelbrock performer intake
-edelbrock 500cfm 4-barrel
-new distributor, spark plugs, wires, coil
-windage tray
-manifolds (not headers)
-all new pistons and rings
-compression should be at least 9.0

what does everyone think. Thanks