My vote is certianly for the 144". I have had two Arctic Cats with 144", however the last two winters I have been running a 137" 1200 Renegade. I believe after a long day of riding the 144" is better on an old back (we are about the same vintage), even on groomed trails.
That said the Yamaha fuel range is terrible with such a small tank. My Renegade I can easily go 120 miles with any worries, and have gone 140 miles and had 4 liters left. You appear to be a Yamaha fan so no slam intened at all, just a comparison.
I think your best bet would be the 144" and a pre-studded track (less wieght).