FortySix12, if you're not experimental, I'm not sure you can do much else, and I do think you'll be happy with the 9.0:1's. If the engine is experimental, you might try 9.5 pistons -- they will run satisfactorily on premium auto fuel. Going from 9 to 9.5 pistons will jack your power up an additional 1.26 horsepower at rated rpm. If you are experimental, you might also try cold induction. Or even the ECI stroker kit that puts an O-340 crank , rods, and low profile rod bolts in the O-320-E2A while using 150hp pistons for a stroker compression ratio of 9.2:1 and roughly about 174 hp at rated rpm, while retaining the O-320 weight. The cranks are available with either O-320 or O-360 prop bolt inserts, and the kit is roughly about $5800. I don't think I'd recommend advancing the timing.
JimC