Are you riding on grass, weeds, snow, ice, packed snow, deep powder, sand...etc and with what; skis, snowboard, mountainboard, etc etc etc
The B5 can pull you if you work it in 8kts or more on smooth ground without much resistance. On ice, it would be pretty good I would think. Same with packed snow. In powder forget it. On sand that's loose, probably not. On packed sand like in Florida with 8+ kts you should be okay on a mountainboard, but you won't be jumping or anything... I would look for a 7-8m for 8kts. Keep in mind you can whip the kite around to generate apparent wind to get going so the smaller sizes should work on slicker surfaces.
(keep in mind I was out last sunday on the ice with my 15m foil! LOL - you may not want advice from me 'cuz I'm craaaaazy)