RE: Size Guide for Uphaulers?
Here is a "scientific" way to calculate needed volume: your weight + gear weight + some reserve (depending on skill and a lot of other factors, anywhere between zero and 50+ litres) = volume in litres. If you've been windsurfing for several years (on what board, btw?), a Go170 should give you plenty of reserve, no worries.
As you progress, you'll want a smaller board, especially if you get a lot of 20+ knots conditions, then a Go will become a big sail carrier only.