Just curious. The 25mm 1.4 is the largest lens I own, as I only shoot primes and the 12-32mm. I don't use a grip on the GM1 and I find it's pretty OK, actually. Please share your experiences with trying out big lenses on this little camera!
I've routinely used the 14-140 ii on the GM1 but I also have a Franiec grip on the little guy. What I find is that the ergonomics change with larger lenses. It's not bad, just different as I principally hold the lens/body on my left palm - that is the lens becomes what I principally use to support the camera rather than trying to pinch grip it with my right hand. This seems natural to me as it is what I'm used to doing with the Nikon and any of its larger lenses.