MF, not Mahindra, but 12X12; 4 hi, 4 lo, 4 creep. I bought a Howse 70" tiller last summer and have used it extensively since. Most of my tilling has been in first gear low range, with some in second low range. I've never felt the need to use the creeper range with the tiller. Perhaps if the ground was extremely dry and hard I would need the creeper range, but I don't generally try to work the ground in that situation as it doesn't do well then. The only clutching involved is starting or stopping at the end of the row. Your gear speeds may be different from mine, but I suspect they are very similar.
Regarding horsepower, I've never sensed that my tiller was loading my tractor at all. It seems to me that the weight of the tiller might be more of a limiting factor than PTO HP in many cases. Mine weighs in at about 825lbs (if I recall correctly) which would be prohibitive on some smaller tractors that had the HP to till with it.