Not disagreeing at all Danny. But there is a huge difference between great kit for birding and knock-about carry everywhere kit like the GM5 provides.
The GM5 is very long in the tooth these days but is still completely unique and valued.
looking around and I see the simple, effective, economical, and still very portable G100 as a GM5 with whiskers. Also the closest thing to the GM5 ethos that can be currently bought.
I’ve played with a G100 in-store and to me it felt like a downgrade from the GM5.
I tried the G100 when it first came out, and had the same impression.
I LOVE my GM5. Have done so since the minute I got it 8 years ago. It's a gem.
But since my GM5 is not young anymore, and I do vastly prefer the output of the 20MP sensor, I decided to try a G100 again this summer, when they had a very good sale on them.
Much to my surprise, after using it for a couple of days, I found it to be a very capable, solid, alternative to the GM5. And, even though it's not as teeny as the GM5, it's still VERY small...and its very little grip makes it easier to hold with slightly larger lenses than the GM5. And, even though I have no complaints about the GM5's EVF, the larger one in the G100 is really a lot easier to see...
Oh, and one other thing: The photographic output of the G100 is absolutely terrific. Excellent color rendition, just a great version of the 20MP sensor and image processor. It really bests the GM5 output by quite a bit (and the 16MP sensors in general).
My suggestion?
It seems as if you have actually decided to get the Sony system. I am sure you will, indeed, enjoy it.
It just seems a shame to get rid of all of your M43 glass, when there is a small body out there that will use your lenses and give you an updated, very diminutive, kit at the same time.
So, I think, if you can find a good deal on one, you should get a G100 body, and keep your M43 lenses and it for an easy/small kit, and go to town with the Sony FF for everything else.
Yeah, I know, I am spending other people's money....but heck, why throw out all of those lenses?
-J