I had your same set-up; the 585 w/62C MMM. Unlike Beenthere, I didn't like the MC519 cart/collection system. The chute would clog with grass clippings quite easy (even mowing every week). That would mean stopping, shutting down the tractor, dicsonnecting the chute, unclogging it and the mower deck by hand, getting piles of clippings everywhere, putting it back together, firing up the tractor and then driving back & forth over the area to suck up the spillage. Pain. The dump feature worked fine but because of the low rear end ground clearance of the cart when dumping I wasn't able to get a pile of clippings. It would have to be dumped like a dump truck spreading gravel on a road and then raked into a pile or moved by hand to a point where I needed it. Due to the mesh liner at the top of the cart cover I found it to be just as dusty as bagger systems. I switched to a power flow 3-bagger system when I traded up to a 4110 last year and never looked back. It can be just as dusty as the cart, and you do have to lift the bags, but it plain works better for my needs, although, you'll find lots of folks here who like the MC519.
I have mixed emotions about the volume of leaves either system will pick up. I found myself making a partial pass of the yeard and then having to drive across the yard to dump them. Not bad if you're looking for alot of seat time but I found it a nuisance. Went with a hand held Stihl blower and a tarp this year and it took less than an hour to do what usually took me 2-3 hours to do with the tractor. Again, just my experience, others may have had a better time of it.
Don't have the mulcher so can't speak for that.
-Norm