I understand when you say that the free race sail is cheaper, easier to rig and also easier to water start and uphaul (mainly because of the smaller sleeve).
That's all true.
But, I've repeated already in many other threads that the heavier weight of a full race sail is only of importance when carrying the sail in and out of the water. When you're actually sailing, it is of no importance and the full race sail will only make windsurfing easier. You get lots of stability and control in return, and this for a huge wind range. You also don't need to be an expert to get the benefits of a full race sail. At least that's what I have found over the last couple of years.
The big belly, wide sleeve and lots of flex are the key factors for control.
Because new full race sails are very expensive and difficult to find in windsurf rental clubs, it's not easy to test them. I was lucky to find good 2nd hand sails. It might be an option.
Test it and you will know the difference.
IS87 / IS101 / IS122 / US147