The longer stiffer Joystick mast is the "best mast" for your 9.0 m2 Retro.
Putting the same 490 cm Joystick in your 7.5 m2 Retro means the mast is
a little too "stiff", so the top of the sail will not be as loose with the same
amount of downhaul tension.
For a 190 lb. this can be a good thing when you are underpowered to well
powered up as your sail has a little more draft up near the top, and will
not twist off quite so early in a gust.
The downside is that if you get really overpowered, the stiffer mast is going
to keep more power in the top of the sail longer, and the sail will not be as
"forgiving" in big gusts as it won't twist off at the top.
I would run the 6.0 on a 460 cm Joystick. That's really the mast the sail is
designed for, and you might find you like the 460 cm in your 7.5 when in
higher wind gusty conditions.
If you plan on getting a smaller Retro, then perhaps the 430 would make
The shorter the mast and lower the IMCS # the softer the sail will be and
the sooner the top will loosen up in response to downhaul tension.
This translates to a sail that is more "forgiving" (and exactly what the designer
had in mind) when out on the water.
Using stiffer longer masts works pretty well on big sail (7.5 and larger) for
It works less well as the sail size decreases and the wind speeds increase.
Hope this helps,