If your on a learning curb, its sometimes best to keep your sail quiver simple with well defined breaks in sizes. Maybe its best to keep a 1m gap between sail sizes. Also, try to stick with the same make model were possible. For instance, one brands 5.3m could be more powerfull/different feel etc than another brands 5.7m. As you get to know what works or doesn't for you, you can start to fill the sail size gaps.
Reading between the lines on your original question, I think your asking, "is the HSM Smack going to work for me" (soz if I read this wrong
). The Smack is a down the line wave sail. Its also pretty grunty (a heavy weights sail). I noticed your on an AHD F-type 106. This board is a fast freeride and best suited to freerie/freerace/cross-over sails (in that order). Plugging a wave sail in wont compliment each other. Think of putting rally car engine in an F1 race car, it'll work, but the way it should do
In the HSM range, the liquid looks to be good for you. Also consider, NP Hell Cat, North X-tpe/Crossride, Mauisails Pursuit, Simmer X-type, Gaastra Remedy/Matrix. All of these will suit your board and will be easy to rig/set and use.
Although its tempting to buy "any old sail" if its cheap, its not always the best thing to do. The wrong sail can hinder progress and generally spoil your fun. Research, research and research the market place. Understand what's on offer and the kit your going to buy. Think about the style of sailing/location/ability before buying anything. Also, try to buy the newest kit you can afford as kit has come on in leaps and bounds.
One of the good things about windsurfing is, the lack of acid rivallary that other sports has, and the willingness of windsurfers to share/give advice etc. So if in doubt, just shout on a WS forum