Or there is the idea that you should buy the largest one you can afford, and never have a problem about flow again. (It always can be shut, but you can't ever make it larger.)
Tial makes very nice parts for sure. I'd think that any gate near or larger than 40mm should be fine for 99.9% of the 7MGTE setups out there. (That V-Band setup is awesome.)
That being said, I have the HKS Ebay copy, and I was testing it last night with some compressed air, and it works great. No binding at all, just smooth operation. It was 130.00 IIRC, is 50mm and has about a .5" valve lift. The housing is quite nice, all the casting work is clean and I'm totally happy with the quality of the part, especially for the money. But, again, Tial makes really nice stuff. If I wanted the ultimate, I'd go that route.
I'm going to dis-assemble my WG and themal coat the hot side, and possibly coat the piston with coatings too. Might as well