hey Ady, Yeah I use the NoLimitz sumo.Gaastra calls for a stiff top mast. I already had a 370 sumo which I use on the 4.2 and 3.7, which seems to rig fine. But for my 4.7 and 5.4 i have a 400 Original no limitz bottom, and a 400 sumo top for a "slightly stiff top", recommended by a Andy at Wind.nc shop.wind-nc.com/collections/windsurfing-masts/products/…. Great sails lots of bottom end power, I picked up three 2015's last year off windsurf and they haven't disappointed.