The v3 is stronger than the v2 but doesn't flow as well.
There is a v4 in the final stages of development but it still needs testing to prove the flow.
V2 with extra welding has given the best results.
If you wanting a k04 your also going to want a fmic, high flow k04 tip, clutch, cupra r fuel pump and maf, injectors, full turbo back exhaust, heat shield for filter and I would also be fitting a catch can and deleting the Evap etc. and also with that extra power suspension and brake upgrades.
I would also be looking at fitting uprated rods just to be safe but that's down to wether you want to.
There's a lot more to upgrading the power then bring on a bigger turbo.