As far as wireless bandwidth goes;
802.11b is 11 mbps max, 802.11a/g is 54 mbps max, and 802.11i draft is 270 mbps max.
In my experience when running ARD3 on your LAN, wired connections are almost always better than wireless. If you're having bandwidth issues with your current setup, first try to lower the image quality slider. The more machines you're managing simultaniously on your LAN, the more available bandwidth you'll need -- justifying upgrading to gigabit hardware.
As far as WAN node management, about the only thing you can do lower the image quality slider to reduce the amount of data being transferred.