I agree with Clark. Feed calibration is a non-issue--the belt is 4' deep. It holds the media down extremely well, and we haven't touched the feed calibration setting since about a week after we received the machine.
We don't print on aluminum for a couple of reasons. One, the adhesion does leave a little to be desired. It's not horrible, but it's not great either. Second, we were printing a job on aluminum a few months ago and had a couple of head strikes. The corners on aluminum sheets tend to bend ever so slightly, and bad things happen. It's not worth the risk to us.
The FB950 and the FB700 are basically the same machine with some firmware upgrades. There are some other small changes, but nothing major. Same inks, heads, print speeds, etc. The 700 uses TCP/IP instead of the VideoNet protocol of the FB950. The 700 also replaces the lour locks (which can be a source of ink leaks) on all of the ink fittings with barbed fittings. It also has the option to print white. Very nice, and very competitively priced machine.
Our FB950 has been an absolute workhorse. We've had a couple of minor issues, with the largest being the scan pully that was slipping on its shaft, and the part was out of stock at HP. We were down a couple of days (and we ended up fixing ourselves by adding a set screw), but HP took the part off of another machine that they had and sent it over.
Right now, we're in the middle of a 1300 bed job (over 40k sf) that'll take a little over nine days to print running three shifts. We're considering the purchase of an FB700 to help out our 950 a little bit.