Yes I've searched and found some old threads with nothing but speculation.
I pulled the heads and pan on a "fresh" LQ4 I recently picked up. It is a Gen III but has the nice floating pin rods and these pistons. Are these stock pistons from 05+, LY6 maybe? or aftermarket. Thanks!

 

They look exactly like the pistons in my 05 I had. The pistons with fly cuts were designed for vvt engines, some just made it into non vvt engines. The valve relief is for the exhaust valves . There are 2 reliefs so the piston can be used on either bank.

 

So, stock...how much nitrous will they hold?

 

Put a better steam tube system on it to keep #7 and 8 cyls happy and the rings will hold 200ish before they have the tendency to butt up against them selves and break lands. File fit them and theyll hold more with a good tune. Its mostly in the tune/afr/plugs if you set up the rings right.