My two cents worth after 3 years with a 4330 HSTC and no immediate plans to switch. When I bought the 4330, I thought I would sell the B-8200, but have been unable to make myself follow through on that. It would be missed.
The factory cab is wonderful, Grand L 40 series are even nicer with improved foot pedal location and a number of trans related gegaws that are nice, but not all that necessary. I REALLY like the lack of direct sun, glare, dust, heat and biting insects in summer and I love shirtsleeves in winter. It is so warm in fact that I frequently have to run the AC to keep defogged. The newer series cab seems to be sealed up better and quieter. Did I mention that I like the cab? Really good chains necessary for winter with R-4's. Duogrips are mediocre at best
Having said that, I regularly wish for more power, weight and width. The 4330runs a 79" kuhn discmower quite well. The M would do it even better with a better sense of security. The M would also be much better for the heavy grapple, but the 4330 does amazingly well. I can work the 4330 pretty hard for 9 hours on 11 gals of fuel. Pretty amazing r.o.i. in that respect. Don't know how the M would stack up. I would make a wild guess of five or six hours on 11 gals.
I have also learned that the cabs are very breakable and have smashed and replaced a fair amount of it. Operator not so smart sometimes. Also,
not great in the woods. Would love to dude it all up like they do in Europe with limb risers, cab protection, skid plates, but that is idle dreaming I'm afraid. Also, every QD implement has required building up the area that the tapered pin closes against so that when loads compress the downpressure spring, the pin does not jump out. I seem to be the only person I know with this trouble; maybe I use it too hard? It just seems like it is only the bottom 3/8ths of the taper that engages it's slot. Have broken those pins too, but if you weld some half inch barstock flush to the opening, problem solved...
So, yeah, I'd like an M, but not at the expense and aggravation of rejiggering all the implements, more fuel, more payments. And one learns to "make do" with what one has. Altogether the 4330 is pretty amazing, and actually it is probably a 4630 now because it will spin the extra hundred rpm that seem to distinguish between the two, not that I run it there anyway, but for the sake of bragging rights. The increase in power from new to broken in (250 hrs or so) was remarkable. Course too, I tried to keep the revs down during the breakin and only rarely run it WFO now. Everyone seems happiest at 18, 1900 rpms, or less.
Some food for thought. Maybe an M with a Cab? That sounds pretty good to me. If you look around on the web, there is lots of second hand machinery if one doesn't mind the risk that used entails. Good luck and remember that anticipation is half the fun. That, and endless hours on TBN.