<font color=blue>What I have noticed with the mid size frame CUT's the manufacturers are putting the nicer air ride seats on them but not on the smaller framed CUT's.... which leads me to thinking the larger frames must ride rougher since their putting the better air ride seats on them???</font color=blue>
The reason you don't see the nice seat on the small tractor is strictly $$$$$$$. The lower the overall price the more the mfg has to skimp to stay competative.
<font color=blue>Do you have a higher center of gravity on the larger frame and does this come onto play? </font color=blue>
Yes, higher COG. It only comes into play when you the operator are sitting higher. Then when the tractor bounces around, you move more (it's all in the trigonometry). Of course if the wheelbase & track are proportionally bigger, you won't move more. This is why a small compact tractor feels tippier than a garden tractor, higher, but not much wider.
I'n college I took a couple automotive engineering classes. If you are looking for comfort, go for a tractor with a good suspension seat. All the wheelbase in the world will still transmit a shock force to your behind. It's up to the seat to cushion you.
None are going to ride like a Cadillac / Lincoln / pick your favorite luxury automobile