Switching from pieced to applique gives you quite a bit of freedom. While certain proportions may be more pleasing, I don't think you have to work in strict block divisions. So as Onebyone says, I'd try a few on for size. My general feeling is that on a queen sized project, 6" is almost always too small, but sometimes it just doesn't take that much.
Just remember that 10" on one side equals 20" total... things can get big fast!
The other idea would be to turn your 66" square on point and applique the large triangles, that would make it bed sized.