I agree with PGHRUBY - don't go to a small diameter tire. With the weight of your 650 a smaller tire will be pushed deeper into the sand. You need at least a 25" tire to keep you floating on top of the sand - with a 22" tire you would be spending more time digging two ditches instead of moving forward.
I know how you feel in not being able to climb the steeper dunes, but the fact is that you have to either add horsepower or lighten the buggy to be able to really perform in the sand. A good target is to achieve a 10:1 weight to horsepower ratio - 1 horsepower for each 10 pounds of buggy+driver weight.
I'm at approximately a 12:1 ratio with my 1100 and it will go about anywhere I point it. I'm still working on getting to 10:1, but I hate eating rice cakes!

phruby I am setting up gotsand with a sweet settup you'll see. He will be more than happy.

thunder I guess I'm one of the lucky ones. But 77 HP that seems kina high. What does the power band look like? Is it pretty even?
I keep telling myself I will never touch the motor for improving power. But you do make it sound pretty enticing.