I love my 084 for milling. It's a bear to use for bucking/felling. My 028 is what I normally use for that kind of job but then we're talking about much smaller wood, usually.
I've used a 440 for bucking/felling and it worked well. I borrowed it from a buddy who uses it for milling. It wasn't too bad in terms of weight. Personally I like my 084 better for milling (liked my 075 better too).
What I did when I started out not that long ago was to buy a used 075 because I could get it pretty cheaply and it has a load of power. I tried it and decided I loved milling. I also decided that it (the particular saw I had) needed too much work for me and was, consequently, dangerous for what I was using it for. So I sold it on this forum (with a clear indication of the work it needed) and bought my current 084, again on this forum, for a great price.
I've heard an MS880 fired up right next to my 084. They're nice (because they're new) but the one at my local dealer was triple what I paid for my 084 (about $1600 as was mentioned up thread) and I don't think there was much, if any, more power coming out of it.
I would buy used/cheap first to make sure you want to do this (unless you're already sure somehow) and I would tend to go with a bit more grunt rather than a bit less, because you will quickly find that you turn an awful lot of your lumber into sawdust, so it quickly becomes clear that a CSM is best used on pretty large (for me, over about 24") wood. That means a bigger saw.
This, of course, is all just my 2 cents, and may not even be worth that.
Good luck!