I flew the 8.5 a lot and then sold it and have flown the 8.0 a lot since. But I did do multiple back to back comparisons. So please take this as my best guess. I think I can hydrofoil with the 8.0 D and the same low wind speed as the 8.5 C.5 and I think I am comfortable foiling with it at 2 knots higher end. I think the comments by others above are very meaningful...and explain Greg's reluctance to assign numbers to kites. Individual riders experiences will vary considerably. All of these kites are so sensitive to input and finesse. If I am sloppy and not precise, my impression of range can change a lot. And they may differ in low end for water start vs low end for maintaining foiling flight, etc. Even if the pull on a straight run might be identical for the two kites in 12 knots, if I turn my foil downwind and initiate a turn while having reduced line tension, the D will turn faster, thus getting moving faster in the new direction...and in that sense give me better low end for that maneuver. So, there are all these different things your do with the kite (and many more that Greg seems to do)...and for me if I kind of guess and average it out, I am as comfortable during the whole low wind session with the 8.0 D and with the 8.5 C.5, despite it being a half meter smaller.