riding lawn mowers on for 6 to 7 acres = dead riding lawn mower. been there done that.
at moment having an old allis chalmers CA tractor with a 60" or something like that belly mower. it is a row crop tractor or rather "tri cycle" narrow front end, were front tires are side by side. with split left and rear breaks. this tractor, operates much like a zero turn mower. it has broke down a couple times, but still runs like a champ. it does have R1 / Ag tires on the rear. and does tear up the lawn some. when i lock up left or right brake pedal and spin around a tree in 3rd gear. but could care less. not wanting a golf course look. just wanting to keep things mowed and looking half way descent. after a rain everything for most part goes back to normally for the grass were i did tear things up some.
the CA is 20HP 4 cylinder gas engine on it. and not one of them little gas engines on a riding lawn mower. this gives me plenty of extra torque and HP to let me mow in a faster gear. and really does cut mowing time in half when compared to old riding lawn mowers in the past.
higher ground speed is a must. for that many acres. and riding lawn mowers just never come close. you might be able to find a commercial zero turn mower that allows for the higher ground speed. and still be able to deal with thicker and taller grass.
there is also a vibration difference getting away from riding lawn mowers vs larger size tractor or ZTR. and that is on a riding lawn mower, once you get off, your inter body is shaking and feeling kinda numb over your entire body for a while. while larger tractors and ZTRs there is less vibrations if any at all besides bumps in the lawn you drive over. those vibrations for me is a big one.
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with above said, pay attention to "gear speed" or rather ground speed for tractor or ZTR. and width of deck. and how long it will take to mow 6 to 7 acres. there is a good amount of online calculators out there. to plug in, deck width, ground speed amount of lawn you need to mow.