no matter what your combo, the higher the compression you can have and still run the gas and timing you want.... the better.

where did anyone say 12.5:1? you were talking a 408. a 408 stroker with flattops and your adverage head chamber size (64cc) you shouldnt be higher than 11.7:1 according to everything i have seen, which is really a little less than that because compression usually isnt is high as advertised unless your block is zero decked or sticking out the holes.

to get to around 10 you want approx 20cc dished pistons with a 64cc chamber head.