I'm looking to buy a Super z Xr-7 72'' deck. I see here a lot of guys have the 66''. What's the advantage of 66 over 72? Also which engine is needed to run these big decks effectively at high speeds/grass? I was going to go with the Kal 25 or the Kohler 27. I keep hearing the Kohler 28 efi is the way to go but it is a lot more money. I have a 20 acre lot to mow weekly and I'm looking for the best buy and long life from the unit. My lot is mostly flat with gentle rolls. I do want to conserve gas and time but also be cost effective. I thank anyone that has any suggestions.