than why upgrade the stock internals? they can handle 250HP with 15PSI. My gt2052 does not produce much PSI until rmps are at 2400. this sucks for a daily but is great for what im going for. my future upgrade is a belt driven compound addition so ill be running 14PSI at 1,100 rpm and hopefully i can get into the 40psi range at full boost.
larger turbo's means more lag. BTW lag refers to the time between rpm's when shifting, we are technically talking about turbo latency or the time it takes from idle to get full boost.
In any case not sure what you want. if you just want to get more boost or get more out of your turbo or go larger, i would try adding a boost control valve and upping the boost first. with your set up you could also run propane injection!
the 2052 is not plug and play. you need a custom downpipe and exhasut manifold. Check out my build with my gt2052
http://forums.tdiclub.com/showthread.php?t=387812
FYI i hate the manifold i got for it as its geometry and port size do not flow nicely but it was a learning curve for me at the time.
My O2J is holding up at my power but its on its way out. Does it smoke at all? if it does not, up the fuel with larger nozzles and a upgrade on your fuel pump with a walbor and a 12 row fuel cooler and larger lines. If your not smoking, you can go further with more fuel and then tune more to get it back down to no smoke. NOS would be a good option if you have smoke at all. I dont like big turbos do to (Lag). Maybe more tune? A cam also. What cam are you running?