Don't underestimate either camera. Especially APS-C vs m4/3 vs 35mm.
granted this example photo was taken with an Olympus E5, but he has recently swapped over to a EM1 and loves it.
The K3 however is actually pretty good for tracking, I'm happy with it and feel its only a few steps behind my D800 when it comes to keeping something locked. The trick is use the selective point focus and get it to track that way.
I don't think with any system you would have an issue. I would look at lenses and which body feels better for you to use. The Olympus with the Panasonic Leica 25mm f1.4 is an incredibly hard combo not to love, and it will be more compact than any similar Pentax kit. However, the K3 and FA 43 or FA 77 will be impossible to beat by anything in the m4/3 or APSC worlds.
I haven't used the EM1, but I do know the biggest disappointment I had with the EM5 was AF in general, not just tracking.