Hi MC Street,
I took a look at the AquaGlide video.
Are you sailing the AquaGlide as a windsurfer (I.E. standing up and holding the sail) or sitting down with the sail held up by lines and a rudder/tiller on the back?
If you can uphaul, tack and jibe the AquaGlide, you pretty much have the basic sail handling and transition/turning round skills you will need on a regular windsurfing board.
At 73-75 Kg. ( 161-165 lbs.) you do not need a really large board.
180-200 liters would be pretty good.
You do not "HAVE TO" go with a large volume board with a centerboard, but since the AquaGlide was designed with a great deal of upwind bias "built in", if you do not get a board with a centerboard,
the "rig steering" skills you developed on the AquaGlide are not going to work.
You would have to very quickly develop some "railing" skills to keep a regular short board without a centerboard/center fin/daggerboard or you will be blown downwind and become very frustrated.
15-20 knots of wind is not reall "low wind speeds" (I agree with PG in your other post that at your size you would need to start out with a 6.5 m2 sail/rig size)
You will find that a 6.5 m2 rig (even with the lightest and most expensive carbon mast and boom) is going to be a lot more difficult to uphaul, but you will be able to pull it up and sail with it (with the skills
you have already.
A GO 155 would be OK, but a larger GO or a Rio M would be quite a bit easier for you to start out on.
The GO 155 does not have a center board or center fin, so that's going to be pretty difficult right at first.
The Rio M seems to me the be the best overall compromise for you.
It has a retractable centerboard, so you can use your current skills right away with the centerboard down.
then swing the centerboard up and get used to sailing by footsteering/railing (which you cannot do at all on the AquaGlide).
If you get downwinded, then simply put the center board down and sail back upwind.
Hope this helps,