actually it would be better to compare LF Envy with RRD Vision, imo. Both are deltas and both have 3 struts. Personally i prefer Vision over Envy, because of the above the bar depower, chickenloop construction and direct connections to rear lines. And imo they both are more stable than passion because of lower aspect, thus being more beginner and gust friendly
Also, imo RRD windrages are understated (9m vision: 15-26knots) both for top and bottom ranges (better safe than sorry?).
eg- i have vision 9m and I'm 180lbs, and in 15-18 knots i would hardly bother using 9m and would go straight for my 12m vision, because i'm sure that on 9m only thing i would be able to do, would be to cruise straight downwind. But- I have used 9m in 20..25 knots without even depowering and actually having feeling "hey! that's some nice power i'm having!"
Still I'm not sure about the top range. I believe it would be in the same 30-34 knots range but vastly would depend on the rider, board, conditions, etc.
btw, if i remember correctly sizes on SS kites were "informal", not actual sizes, so it might be no wonder that somebody uses 10m as his biggest kite... also it could be that he just kites in 15+ knots.