Hard to Downsize
The secret is to not switch, just buy a cheap E-PM2 + few primes. Also get rid of heavy zooms on the 5DMKII and stick with primes as well. 2 Bodies covering two different focal lengths has you better covered in IQ, weight, cost, compared to a single zoom or trying to juggle prime + zoom or lens changes during vacation. ........
Thanks for your idea-packed post. That I might actually save weight by by buying a second body plus a few primes is something I did not think of. Not sure it works in my case, and is probably cost prohibitive, but the 4/3 option is appealing.