I saw one of your posts earlier about SpaceTime Calcs, I was wondering if you tried running SpaceTime mobile? There is a version for Palm OS 5 which should run under the Garnet VM. http://www.spacetime.us/palm.htm. They also seem to be working on a linux version, so they may be smart and port it to nokia nXXX/armel.

Not sure the other two machine choices will be much better. The Via C7M ULV is not very good, I would rate the 1.2Ghz as equivalent to about a 700Mhz pentium III, and has very poor battery performance. The Nokia N800 would be about a 266 pentium II but with much better battery and no heat problems. Unfortunatley the C7 is going to generate alot of heat, needs a fan for(which is pretty loud on the WiBrain) and will still be pretty hot to the touch, (one of the reasons I've been avoiding UMPC and MID type machines, besides not being pocketable)

The AMD Geode LX 600Mhz in the Everun will not generate as much heat and get much better battery life than the C7M ULV, but I would put the performance at about pentium III 450Mhz.

The benefit of course in both of these, is access to x86 codebase, so a huge choice in software. Though it might be worthwhile to wait and see how the Atom machines stackup?