I have played with 2 920's wirelessly and could not get a decent 640x480, so lowered to 320x240 and 10 FPS. It still was choppy, and seemed to not get above 5-6 FPS net per camera. Have now gone back to wired, as the Wireless-g on the 920 is seemingly not very quick (even against wireless-n router). Awaiting results on the new 1130 (methinks), which is supposed to be faster as it is Wireless-n.
My advise: keep them wired if image quality or motion sensing is important.