The suntour Vx-GT will do amazing stuff if 7 speeds is enough. I have odd tastes in cassettes and am experimenting for a future bike build. Current idea is
13-14-16-18-21-28-36. I was wondering what derailleur I would need. Since I have several Vx-GTs I thought I'd give it a shot. Man it just worked perfectly!

7 speeds and the truth right here.

No issue at all climbing this on a 1971 Raleigh professional.