I'm in a buggy and never been on a board, but all I have locally is grass (football pitches) to ride on. I have older versions of the 2-, 3- and
4-meter Hornets, but at 76kg 5'8", I find that the 2m and 3m are rarely enough to get me moving on grass. (Lately, almost all of my riding is on
sand.)
While flying, the back lines are always slack, but they do help speed up a turn. I've also had them on a turbo-bar, and didn't really find a
difference in their handling. I appreciate that all of them have the same flight characteristics.
Even on sand, their upwind performance isn't fantastic, but good enough so that I never have to walk back to my starting point.
Short answer: the 4m will likely do the job for you, but it may be worth considering the 5m.
Go ahead... tell me to "go fly a kite!" Please!
Howard - used to be KC67
Fly: A quiver of Lynx' and Cores (did someone say "Pansh"?), a couple o' Arcs, and a Rev to remind me about control
Ride: PL XR+
Where: 43.857899, -78.941661 and 38.970951, -74.828922