Did you read my post, where I said we went with the Z800 due to the need for more than 32GB of RAM?
Have you actually used both machines to develop a worthwhile opinion of them and a comparison resulting from that, or are you just going to post what C|Net says?
Yes, there is more RAM capacity. There are also (4) 3.5" bays inside, just like the MP. There are a couple more slots, though they aren't really in use on either machine, so pretty much a moot point. The additional 5.25" is kinda weird too; I've never used more than two, and haven't used more than one in over 5 years. I guess it's a selling point for some reason.
Here are the quickspecs for the Z800:
http://h18000.www1.hp.com/products/quickspecs/13278_div/13278_div.HTML#Overview
The MP is easier to work on in terms of getting RAM in and out, as well as drives. YMMV. The MP's we have mostly have 3 drives in them, 2TB a piece. We're not exactly hurting for space. The handle thing is very subjective; while the HP's handles are smoother, you can't grip them as well as you can the MP's. To each their own, I guess. All of the machines have the FX4800 in them, so that's a draw.