My E-M1 arrived today. I had pre-orders with Amazon, B&H, and Olympus but ended up buying one from a member. I have an E-M5 with the JB Grip, and the differences in weight and dimension are negligible. The EM1 is 15 grams heavier, a cm wider, and a cm shorter than the EM5 with the JB Grip. I travel a lot and walk with the EM5 in my hand and the JB grip makes it very easy to carry it around all day. My sense is that the EM1 grip is more comfortable to shoot with but less comfortable to carry around all day. The grip protrusion is not completely vertical so you only have 3 fingers to grip it when you walk and on the JB grip I had four. The camera powers up and operates much more quickly and smoothly than the EM5. It is noticeable in every function. I took the camera to a high school volleyball game today and tried out the new C-AF-TR function with an O45. It seemed to track in CD mode and I can't figure out how to get it to work in PD mode. Overall, autofocus feels a little faster than the EM5, but its not a big difference. The viewfinder is larger and overall more clear. It is brighter too and you can see the action better. One thing I love is that when you put a MF lens on the camera it automatically detects this and switches to MF mode. No more futzing with mysets to shoot MF lenses. Its easy to set the function buttons too. It seems a lot of attention was paid to making this camera really easy to operate. It is far more intuitive than the EM5. The JPEGs looked the same to me. Couldn't see much difference with the EM5. I will take it out and shoot in daylight tomorrow, and report back more results.