I think a 5x3 would work as long as you set it up so that the extra room is to your left and right. 5' would be far too far to easily reach across. If you have space on each side (left and right) then you should have enough room for cards, extra figures, etc.
Alternatively, if you have a large table that this is just going to sit on, then a 3x3 play area that sits on a larger table would be good as well.