As said mahle are fine, and a excellent piston, need to get valve pockets done as you will need a different inlet cam ideally for 500bhp.
One thing you should consider is whether you intend to do any further mods power wise, as this could affect the CR needed at present.
As a general rule as high as you can get away with is the answer, as this will give far better off boost power, married to a decent mapping job.
tabetha