the bar presure is almost the same as the 10m if you have riden one of them but the steering presure is slightly increased due to the 12m having the same bar as all the smaller kites. The bare presure on the 14m however is a lot lighter and steers verry easily with the larger bar. JN kites make the MR F.... which is also a delta kite i have riden one and the bar presure is a lot lighter and it also has tuning points on the wingtips to adjust for steering the performance was almost the same and they come with one pump.

The bottom end power depending on your weight and board size would be around the 13-15kts. but for the lighter conditions I would always ride th 14m as the 12m needs to be depowered and flown a bit to get going and stop backstalling, (for bigger guys 90+). wher as the 14m is a tractor.

See if you can find one to demo to get a good feel of what they are like, I hope your back can handle them as they are a fantastic kite.