KTM,
25HP 4x4 would be the minimum I would reccomend for a 2.6 mile driveway with hills, you do not want to be undersized. Of course you want to match the snowblower with the machine size. I just sent a 25hp and 27hp machine to upper state NY and they put 5ft and 6ft blowers on them respectively. Going bigger is a function of price. I also would not rule out a Mitsubishi or Kubota in that hp range. Specific Yanmar models I would reccomend:
YM 2210D 26.5HP
YM2610D 31HP
FX22 27HP
2310D 28HP
Best Regards,
Bob