I have done 12 inputs via 3 LFG4 cards. It is possible. I would recommend using a 2008 mac pro for this with an 8800 GPU.

If you are trying to switch 10 cameras though, wouldn't you have a TD running their own switcher? Wouldn't it make more sense to take a second ME from the main switcher and feed it into a single input than to have a second switcher just for Catalyst? Or is this pre Cat Switcher the only one?