I also vote for the C1xx phones. I didn't realize they were still available
in such large quantities, which itself is a huge advantage IMHO. But the
simpler development model and needed software stack, along with major power
advantages seems too good to ignore.
I don't know if the previous discussion/decision regarding NuttX stands.
This (limited) RTOS benchmark looked interesting to me:
http://www.yagarto.de/projects/rtoscomp/index.html
I am very interested in contributing what I can to such a project.
Scott