The Goldstar was the smaller forward only ESC (The Silverstar had the reversing relays which elongated the speedo somewhat!) There were 'Turbo' versions of each which both had lower motor wind limits. I can't remember what the wind limits were off hand but I wouldn't go any lower than say a 17turn on a
non-turbo Speedmaster ESC. I think I used to run a 15t Trinity Onyx on my Goldstar, but eventually blew the brake FETS
Going from the instruction sheet I have in front of me; the RX voltage is 5v
Hope that helps