Let me see if I can get a pic. I just looked at this yesterday. The two guns are VERY similar in size in all aspects except width and weight.
The R-9 is a bit heavier (12.8 oz. unloaded v. 7.2 oz. unloaded), but not "heavy" at all. The R-9 is noticeably wider (.82" in the slide rather than .77, but the grips add a bit more width).
The R-9 is a bit bigger than the P-3AT, but really not much.