I couldn't wait, so here is a pic of a standard and a hi-flow, side-by-side (hi-flow is on the right). The windows measure the same. And except for the hi-flow having a darker finish, I can't see a difference. The only thing I can figure is maybe the opening on the threaded end, but I'm not going to tear it up to measure it. Hopefully, I can get the hi-flow in this week, and see if I can richen up my A/F.