Olympus E-M5 maximum burst depth with smaller jpegs?

Well, the answer is complicated. Yes there is a medium fine setting. You can also set the pixel count for the medium setting to 4 different sizes. The super control panel only offers a subset of the many size/compression setting possibilities, and you control which subset is offered deeper in the menus. You can also control the frame rate for the high and low speed burst modes. For example, the frame rate for the high speed mode can be set to 5,6,7,8, or 9 fps. At high speed 9fps on my camera, in medium fine, I get maybe 20 shots at 9fps, then the frame rate drops to maybe 3 fps but seems to keep going forever. Totally guessing there, I didn't time it. I held the shutter down for a while and got 178 shots and it was still going.  I did try a burst at large fine and compared it to medium fine, and I did get more shots at 9fps in the smaller mode. It is possible that if you select a slower speed, such as 5fps that you might be able to get a lot more shots before it slows to 3fps, or it might even fire continuously, I didn't try it. Not sure exactly why you want to know, and I don't want to wear out my shutter.