Hey dafish,
Simple answer:
- Get a smaller board
- Edge harder
It sounds like we're at a similar skill level. I have a slingshot rev2 9m, and absolutely love it

. I've flown it from 15 knots to 33 knots, and at 67kg and previously on a 130x39 twintip, i find that i start getting overpowered at 25 knots. From 25-30 knots my legs burn from edging so hard. Over 30 knots is frustrating and dangerous (for me). I find that the 9m actually flies reasonably far forward in the wind window, which makes it relatively easy to edge out the power and control speed, and gives the kite a decent wind range.
Here a few tips that have helped me to control speed:
- Ride slower (although this is useless if you're already going fast

)
- Edge upwind immediately after a water start
- Get a smaller board for those high winds. It seems that a 141x42 is too big for that wind and kite combination (most people at your weight ride a circa-135x40cm board as their 'everday' twintip)
- Commit to a really hard edge. It might take a while to stop or slow down, so just keep edging. If you know how to do a slide transition, try and adapt that technique to controlling speed. i.e. instead of stopping you just slow down.
Hope this helps. Good luck.