Which first windsurf board

Question
QUESTION: I can SUP fairly proficiently but I decided to take up windsurfing to get away from the crowds at the surfing lineup. I'm live at Hanalei bay Kauai, not a big wind place but usually reliable 10-15 knot tradewinds with gusts to 20. One side of the bay is windier with no surfers.
I'm learning on an old Mistral superlight with a 6.1, I can reliably uphaul and get underway and steer but coming about is near impossible as this board is just too tippy.
I've decided I need a proper board to learn to gybe and tack.
I am looking at buying a used board from one of the schools on Maui.
The boards I am being offered are basically a choice between the super wides like the 230L X 100CM wide Naish Kailua, Starboard Rio and an older Fanatic Viper or the step down to the 180L X 85CM wide versions of the same models and an especially good buy on an RRD Easyrider 180L X 85 CM wide.
So the question becomes which one?
I've read that a larger board can get me planing quicker in light winds but reservation is those 100CM boards seem awful big.
I'm 6'5" about 215-220 lbs, that's about 100 kg
I picture myself planing across the bay in the summer like the Hobie cats and perhaps playing in some smaller waves in the winter.

ANSWER: I need to know what the volume in liters of those boards in order to give you the best advice.  Find out how many liters each board is and get back to me.

---------- FOLLOW-UP ----------

QUESTION: Yes, it's basically 230 Liters volume X 100 Centimeters wide vs. 180 Liters volume X 85 Centimeters wide, the wide vs. the super wide.
All boards are 260 to 280 CM long.
So the question is are these 100CM wide boards good for anything but learning and are the 85CM wide boards wide enough to learn on?

Answer
230 liters is basically a learning board.  180 liters is good for very lite wind only. You would likely grow out of these quickly once you become more proficient. Based on your weight you would be better off buying a board in the 160 liter range which would give you more of a short board experience.  You should buy a board you can stand on and uphaul for your first board but one that is not too big.  You should really demo the board before buying it.  Are you able to demo it? If not you are taking a big chance you may not like it regardless of the size. Hope this helps.