Tillers need surprisingly little power, especially if the soil has been worked before. I run a 48" at only 1/4 throttle with my BX. No power issues whatsoever. Covering your wheel tracks should your primary concern followed by the area you need to turn over. If it is a large area and you want to get the job done quickly, that's when you need more HP---to move at a faster forward pace. Otherwise, take it slow and your machine will handle a 72" just fine. Moving slower will also give you a better result no matter what size tiller you use. Only you can judge whether the extra width is worth the money for your needs.