I dont have experience with the newer model GO's, but I have an older (Circa 2005) GO 165L (90cm wide) and it is fantastic. My kids learned on it, my wife sailed it, and I still use it for light wind fun days with a large sail.
Mine has the screw-on side boards, which the kids used at the start, but discarded when they go a bit better skilled.
I would be pretty confident in saying that this GO 151L, 86cm wide board will suit you well from what you have described.
With your size, I would recommend either if the larger two sail sizes. The 5.7m will be easier to handle and uphaul, and the larger one will give a bit more power for getting to planing in the 12-15 knots of wind. The 5.0m is proably too small once you have got the hang of balancing your weight against the sail and leaning back and you would need stronger winds to get planing which means rougher water and more difficulty uphauling and balancing.
Have fun, and good luck!