Hi Alex, my gf has a relatively small head... that's why. It is not too big actually.
... and it is really light, much lighter than my k200d. and is very balance. The grip, is more comfortable than k-7 (when I hold the k-7, I thought its grip is very comfortable, but 645d grip is even better than k-7).
Rush, the view finder is large, clear and very bright! I am surprised when I look through it.
btw, all 645D shots are with my k200d and 35mm macro, shot through glass... don't have much time to frame and focus, just try to find an angle that has less reflection from the glass to shot. The size comparison shot is with the 100mm WR that I get to put on my camera to try out that day, and the last two shots are with k-7 that I try out.