I have a 2005 Severne NCX 6.5 sail that I have used with my Futura 93. I also have an SDM 430 Gulftech mast that I tried on the NCX. It doesn’t work so I doubt your Gulftech RDM will work. I ended up getting a Fiberspar mast based on Severne’s recommendation.
The performance of the sail has been very good. Not great power, but great range, fast and very light. I find the 6.5 NCX very easy to jibe, backwind sail, or do light wind hellitacks or upwind 360’s. The sail just feels much smaller then a 6.5.