The 2GR platform is stout from the factory and capable of delivering an exceptionally long service life. These motors have a forged crank, forged rods and 6 bolt main bearings from the factory.
The pistons are cast so that's really the achilles heal if you add too much power or boost on top of the factory 10.5:1 compression. Jubu claims that the pistons are susceptible to breakage when they've tested tunes that delivered in excess of 500NM of torque so it's interesting to hear Greg's experience. There are plenty of stories online about twin turbo 700-800 HP 2GR's with the stock block and crank but new forged rods and pistons so there's a ton of potential if you have the funds and that's how the Jubu short block comes for those that want to build the motor to that level.
I think the original poster has the right idea for his situation. If you have to pull and rebuild the heads anyway, why not exchange your cores for new heads that have been ported and built with a high performance valve train to support higher RPM's. Seems like a natural without breaking the bank.