The IR remote works well navigating Vim-ATV, keyboard directional keys also work well. On scroll wheel, I have to be careful not to scroll more than about 2-3 clicks or it does what you say, don't know if that is typical on ATV, as I think it was designed to work with remotes, primarily.
Side scrolling in Google Play with keyboard direction arrows or IR works very well. Mouse works well too, but if there is any inadvertent up/down mouse movement when trying to side scroll with the mouse, it will break out of side scroll and move up or down. I am not overly familiar with ATV, but I would suspect this is normal.
I get 45~60 Mbps on the Pro on 2.4GHz. But of course this is on a different WiFi module, AP6255(Pro), AP6212 Vim 8GB.
Have you tried Wifi Analyzer to see what channels are best received by the Vim? Then you could change the channel on your router for best performance.
Also, check the antenna's connection to the PCB to make sure it is well seated.
Superceleron does not yet have the Vim 8GB, but that may change.