Stock pistons are great on the GZE's (factory forged), as long as your AFR's aren't too lean you shouldn't toast them. Admittedly though I'm probably not the best person to recommend but what you sound like you are doing doesn't sound unachievable considering what's already been done to 4AG's before.
If you are doing rod bolts and possibly rods, I'd been looking at your rings as well. Apparently factory are cast, and whilst they are awesome at handling boost, there will be a limit to where they will inevitably fail.
If you aren't cracking open the bottom end you might be fine as it is, if you are though, get a set of chrome rings put in and have the block honed to match the rings, so you get proper bed in and very little chance of blowing them.
There are previously SC14 GZE's floating around the forums running a good 140kW at the wheels on stock cast rings, now gone s15 turbo and running 170kW, nothing else changed in the bottom end. Food for thought.
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