dang, with vf39 and exact same set up, your car probably would have made around 260-270 whp on the mustang dyno with pump gas. That's with assuming that a stock sti reads around 210 whp on that dyno.
your mods are really good though. I don't think the intake and turbo inlet is that much of a restriction. I'd think the high flow cat is more of a restriction, but still not that significant.
to me, for power wise the td04-19t seems to be closer to the stock td04 than vf39. The spool is slower for the vf39, but probably by only few hundred rpm, maybe 400-800 rpm?
in my honest opinion with no disrespect, I don't think the 19t upgrade over vf39 is worth it because it seems like the 19t won't make nearly as much power as the vf39 and the price for a used good condition vf39 could be cheaper than having a stock td04 upgraded to have the 19t wheel for $325 plus any rebuilding costs. It is true that the vf39 lags more, but i believe i will enjoy the higher mid range and high end power of the vf39 when going wot on the freeway on ramps haha.
I could be wrong though, just my thoughts.