There is a guy far more in the know on this board than you or I that said the GTX3576R is equal on spool to the GTX3076R on spool and makes a decent amount more power. I’m pretty sure his info is solid and not from some “poor” comparison.
As 94AWDcoupe pointed out though, if you want to compare GTX to HTA, you gotta pay attention to more than just the names.
One more FP turbo to consider:
HTA3073R - 54/73 - 54lb/min
Best comparisons I think you could likely make though:
HTA3073R and HTA3076R vs. GTX3071R
HTA76R for a slight power gain, HTA3073R for slightly better spool.
HTA3582R vs GTX3576R
Slight power advantage to the HTA wheel with response likely going to the GTX.
Simple fact here, no turbine housing can make up for the low flow capacity of the GT30 wheel. The bigger the housing, the lower the efficiency anyway so you are really going the wrong way stuffing the small wheel in a giant housing to make the GT30 work with a compressor wheel over 60lb/min.
HTA3586R vs. GTX3582R
Not a clue how each would come out here as the GTX wheel flows like crazy but also has a smaller exducer. It seems like the aero was targeted for all out power though and this has hurt response. The HTA seems to be designed aerodynamically around spool improvements but is larger to reach the flow targets.
Realistically though, these are all great turbochargers and the difference in performance between them is likely to be very minimal. I personally prefer a turbo that has come straight from Garrett. On the other hand, I've used 3 FP turbochargers and all three were great turbochargers. You really can’t go wrong with either.