I'd agree with getting the 8.5 m2 2008 Retro.
Tuned right on a std. diam. mast the 6.6 Hucker can provide
nearly as much power as a 7.5 Retro, so while 8.0 would be a
more "normal" quiver spacing, I think you will like the new 8.5 m2 Retro
as your next larger sail.
I know at least 2 other 6.6 m2 Hucker sailors that have 8.5's as their next
larger sail and they seem to think this combination works well.
Hope this helps,