As an owner of two MX6000s (still have one) and an M6060 I think you're making a great choice by moving up to the M6060! The M6060 is way more tractor than the MX6000 for only a "marginal" increase in cost. They are such different animals and I'm lucky to have both with no intention of parting with either.
That said, if I had to part with one it would be the MX for the simple reason that there's nothing the MX can do that the M can't, but there's plenty that the M can do that the MX can't. I have a lot of mowing to do on a my very hilly property and I've done it with the MX and Land Pride RCR1884, but it's way more efficient and way more enjoyable with the M and Land Pride RC3712. The M handles the hills and load with ease but the MX is taxed to be honest.
The M rides better, is more fuel efficient, has a bigger 4-cylinder engine, has a nicer control layout (ergonomic), nicer (smoother) controls, has way more torque and usable hp, pulls better, more PTO hp, has a better HVAC system, has external lift cylinders, way more lift capacity at both ends, runs cooler, is much more comfortable etc., and don't forget that you can buy a programmer that will turn your M6060 into an 80hp+ machine with no regens to deal with.
I added Creep range to mine, along with a third rear remote, third function, wheel weights, Rim Guard, front weights, top-n-tilt, and swapped out the front wheels and tires for 320/85R20 Farm Pros. I have close to the perfect tractor for me, but as I've said before, had I ordered an M rather than bought off the lot, it would have been the M7060 with F18/R18 rather than the F12/R12 that I have. Having closer gear ratios is a good thing but the F18/R18 has worked well for me so maybe it's a nice to have rather than a need to have.
One more thing, peak torque is at 1,400 rpm and with the programmer you can run at that rpm all day long without any issues.