Nearly all the freeriders use RAF sails ( no cams ). Even Sean O'Brien uses a Severne NCX when not training for PWA. A lot of windsurfers are into GPS speed sailing hence why there are so many Cammed rigs around. They like to be the fastest.
I don't know anything about the other brands like North etc. as I've only owned NP since 1995. Hopefully someone else can help with your North.
The Go 144 is quite a detuned board so you wont be getting into to much trouble in the lighter wind. Your Fusion is a perfect light wind sail in 7.2 for QLD on that board. You won't plane until you have a solid 13 knot gust with either the 8.2 or the 7.2 then you should keep it planning down to about 11 knots when already planning.
The fin is a good size for the G144 will help in the light stuff. Could go smaller 38/40cm as you get more efficient or it is a solid 15-16 knot breeze. I was 90kgs last year so you will be fine with the 7.2 and you really do not need anything bigger. Remember the fusion 7.2 has the same power as 7.8 -8.2 sails and is a lot lot easier. What is the boom measurement on your 8.2 ? When comparing a board you need to know the width and 30 cm measurement at the tail, and sails the boom length and luff gives you a good indication of what wind it will be best for. Some 5.5 sails have an incredible 8 cm difference in boom length.
Don't worry to much about the different brands you have. Usually a light wind sail requires a 460 mast ( not the Fusion

). Typically 6.0. to 6.5 sails are on a 430 and 5.0 to 5.5 on 400 masts. So you will need more than one mast anyway. The important thing is have the right one.
Since you already paid for a new Fusion get the right mast for it and it will last for years. You could sell the 8.2 or trade it in on the mast or another sail you need etc. If you decide you like the North 8.2 better then get the right mast for it. Most windsurfers get a feel for a brand and stick with it. The three I sail with at Redcliffe all have one brand in their kit. One is on Ezzy, another on Loft, and another on Neil Pryde.