They identical turbos as said before only differance is the exhaust housing/bearing which doesnt make much diff at all really
35 spools faster but lack top end (p15 rear)
34 have more mid range punch and more top end but slightly less responses (p18 rear)
You will hardly feel the difference maybe around 200-400rpm diff to full boost?
Which ever you get make sure you get an uprated actuator to hold boost better like a HKS/Forge Motorsport
However if you launch your car you will feel it, 6K limiter launch
I assume you have a TD04 now? I would get a VF34 coop with a STI top mount and 555cc injector. DONE.
I wouldn't get the p20 housing either like some of the other here as I don't do much "freeway" runs or anything that requires more top end stuff. Bigger rear housing give you more top end and
slightly more power and lag