Mahle are the best pistons available
I suspect if your tuner has seen bad ones, it was probably because of a bad tune, or other factors. I would take Wossner as a second choice and then Wiseco. I don't like JE. I've used them in the past and they were sloppy in the cylinders (bad piston slap when cold) and one of them scratched a bore in my VR6 and basically ended that block
I ran Wossner in my VR6 turbo for 60K miles with a lot of boost. After that mileage they were spotless, the coating was still on the skirts. Great pistons.
The OEM pistons are a special pressure casting with good quality material. They can take a lot of abuse but do give up eventually. The main advantage of 4032 and 2618 piston alloys is the material is denser than cast, so can handle heavier loads before cracking. Usually with aftermarket pistons, you will see a thicker top ring landing and reinforcements in the gudgeon pin area, which adds even more strength. And they are lighter
You won't go wrong with Mahle. They are OEM supplier to just about every high performance car maker out there
ARP head bolts, great move! Get some ARP rod bolts as well, although they might come with the Bar-Tek kit? I do like Bar-Tek, again, you can't go wrong with those guys
9:1 is a little low for the compression. You may find engine braking reduces, starting takes a little longer and off boost response suffers a little, but you may not notice these things in a race car
But the up side is you can run more boost safely and also make up the compression loss with more ignition timing