I think there's a pretty good chance that you'll be happy with the GPS performance under V21y. I've seen a number of reports that it's better. My own experience is that it's better but not perfect. I have gotten a number of 15-second fixes, which happened only extremely rarely under other ROMs. However, it does occasionally take 2-3 minutes, which is just what I was seeing before I installed V21y.
I hope so, because I do like the phone. The performance, camera, screen quality and form factor are all very good imo.