I own the 2012 12m and 10m Razor. In my last good wave session (6-8ft. faces and gusty sideshore) I started with the 12m and switched to the 10m asap. Why? I was getting frustrated using the 12m (albiet somewhat underpowered at times) in the waves. It just didn’t turn fast enough for the conditions. It was a big adjustment from using a 2011 6m in the previous 2 sessions. Anyway, the 12m Razor is good for a big kite, but the 10m is significantly faster and really seems to be the money kite in the razor line up. The 12m has more ultimate low end, but in 12-14knots working the 10m hard will get you up and planning and achieve the desired result. Personally, I really like the 10m. It has great low end but turns fast enough to be great in the waves and loops fast enough to catch you before landing those big kiteloops.
Bottom line- if you have the wind, the 10m is more fun to ride than the 12m.