TGP 3SGTE pistons are available in a 0.5mm oversize. . .
about $250NZ each to be exact
Cheapest non TGP cast pistons are NPR\Teikin Ring\Piston combo at $220NZ for full set of 4. (from eBay)
Also available in oversize.
Im putting some in mine very soon. Like any cast piston, if its tuned correctly and you arent getting detonation it should hold up to whatever youthrow at it, more than what the stock MR2 fuel system can support anyway.
I had the option of forged but for the power level I was seeking (270-300 RWHP) and the fact my car has cost nearly 10K in the last 6 months now im faced with a rebuild I just couldnt justify the extra $500 for forgies, better spent on other thing like waterpump, head gasket, knock block for my Link.