Well Alan, since I remember your impressive posts awhile back on CB radio range, I know you're way ahead of me when it comes to radio/electronics aptitude, so it's your call on which one to get and I'd probably lean towards the 857 in your case.
I remember the HRO salesman telling me that the 817, 857, and 897 were all essentially the same radio, with the 817 minimized for the backpacker who could live with QRP, while the 857 is virtually identical in performance to the 897, minus the on-board battery. I believe the 897 has an available power supply that can plugged into the battery space, which would make for a compact foot print and less cable clutter (although, I'm learning that clutter seems to be unavoidable with this hobby).
I came close to getting the 897, but went with the FT-450 to learn HF on after I realized how cumbersome the menu system on the 8x7 radios is, especially for a noob like me, and wanted to minimize the frustration quotient. Once I get the hang of things, I'd like to start packing the 817 and try it out on the 10,000' peaks in my area, but I need to know what I'm doing first.
I'm in the process of building a compact, transportable shack using an 8u rack mount case, with the 450 and 2900 permanently mounted inside with power supply, rig runner, power gate, antenna switches, and some AGM batteries. With this setup I'm hoping that it will allow me to use the radios with less clutter, while still allowing me to store it totally out of sight so it's one less thing for my wife to complain about.
There's so much extra crap that goes along with getting on the air, it's not just the radio. You've got dc power supplies, batteries and cables, antennas, feedlines, tuners, switches, meters, etc.. Things get a bit more complicated in going from VHF to HF.