I have the 15, 11 and 7. I find that there is no problem with the spread between the 11 and the 7. I find that I can use the 7 in surprisingly light wind. I feel that the Slingshot Rev is a great kite because it has similar flight characteristics no matter if it is set for full power or full de-power. I have yet to pump up two kites in one day since getting the Rev's.
I have 11 and 9. Kinda close but works for me. I like to be in the sweet spot, agree they fly great powered or depowered. Although I don't own a 7, I don't think I could go from the 11 to the 7. When set with front lines one knot longer than back lines, kites have amazing low end. I have gotten use to the below bar sheeting and really like it, easy to adjust. Keep the c-loop on your weak hand side and I have experienced no mistaken releases. In other words I am right handed so I have the release aimed to my left. I de power with my right hand. Great turning, stable and smooth kites. Self launching works well, landing not so good since the nose sits off the beach when at rest, wind tends to get under it and lift it, only bad habit I have discovererd. My big kite is an '08 REBEL 14 and lately I have been using it less and less since the REV gets me going in 15 knots I think with a 555 135 NOBILE @ 185 lbs.