HP does kinda matter, generally a tractor of these sizes should weigh around 100# per HP.  Therefore the heavier the tractor is, is going to affect the ride a little bit, the lighter lesser HP tractor is going to work its but off and probably have more slippage which could likely have an adverse affect on the ride if that is what you are mainly concerned with.        Although since track tractor don't experience powerhop it may not be that noticible, not sure how hard your NH3 tool pull's in your soil conditions.         I will be curious to know what you like the best when your done!
   I like a great ride and nice creature comforts but I really like the one that covers the most acres per hour on the least amount of fuel!