i would only be considering it with the 75-300 lens, as it would purely be used for distance wildlife shots and nothing much else. sounds like a waste of a camera i know but for me to get 500-600mm on the canon its pretty much the sigma or the tamron, both of which are bloody huge things. whereas this combined with the 75-300 zuiko would still be relatively small. also 99% of the time i would be shooting from static locations so mounting on a tripod would be most likely scenario ( my benro travel tripod would be ideal ) . again with the big sigma or tamron i would have to dig out my very heavy redsnapper tripod for stability so even more weight to consider.
the only real difficulty is finding a
second hand em10.. seems to be very few out there body only and as having one with kit lens just means paying out extra cost.
the 75-300 on amazon.de is 307 free shipping. so that gives me around £300 to find an em10 body