I have an L47 and many attachments. I chose the model for its relatively compact size to FEL capacity over most AG models. (More on that in a minute).
When comparing the L47 and M62 models they are close in size yet I went with the L47 because it fits into my horse barn with raised breezeway. It barely fits under the sliding doors frame. It is so close to the top of the cab in fact I cannot measure it, like perhaps 1/100th of an inch! It allows me to drive right in with various loads, whether freshly milled stacks of slabs for seasoning, or loaded pallets etc. Quite capable. Obviously I extend the backhoe out a bit to lower the highest point. The M62 transport height is listed at 136", or 30", over the L47. I believe this to be a measurement to the top of the curled backhoe, and not the plastic cab top. Other dimensional comparisons to the M62 are to be considered (from Kubota pdf): Ground Clearance 12.3 vs 13.6", Turning Radius 9.2 vs 10.8', Nose to Tail 234 vs 253". Very similar numbers actually. I feel that the M62 is a turbo charged L47 with engineered robustness to handle the increased power.
My experience with moving logs has been good. I recently maxed out the FEL with pallet forks on a Giant Sequoia log, very heavy and wet log. I only managed to raise it about 4', at full roar it couldn't get it any higher...just barely enough to get onto my flatbed. It was well over 1300kg. I did it without the backhoe attached, just a flail mower and half filled tires. We have all seen those videos of dogs carrying such a large treat/toy that cantilevers their rear legs up...that didn't happen to me even though I would have preferred to max out the loader with the backhoe mounted.
PTO is another comparison as you have already mentioned. I have had no problems running a large flail unit with hydraulic side shift. I run 2500 rpm to maintain the recommended 540 unit rpm.
No final model recommendations from me, just trying to throw a little data at you. I do recommend you get all the bells and whistles when it comes to auxiliary hydraulics. The Top and Tilt is wonderful when road building, and the backhoe with hydraulic thumb can be very useful for rocks and branches. You mentioned an FEL grapple, I believe both models come ready with that third function.