I think John (jjphoto) has made some good points. Plus, he has used both cameras.
I would highly recommend trying an R8 before you fully commit and get rid of the OM system.
You'll often hear people say that a certain camera "just feels right in my hands."
It sounds like you're in search of something larger. I've always felt that way about the Pentax MX. Lovely camera, but just a tad too small.
But definitely hold the R8 in your hands, if you can. I think it's a very handsome camera. Never held one, however.