The songs I do in my band that I can't do on a 4 string are poker face (actually possible but not as easy), baker street (again possible if I miss out some of the accents), Brick in the wall, Moondance (yes, it can be done on a 4, but if you have got used to it on a 5 it is a real faff on a 4), black magic woman (for the same reason).
There are some others that if I am paying attention I can play on a 4 string without messing up, but would seem a bit odd to limit myself. I used to play with a 4 or a 5, but because we randomly change songs at the last minute I have no idea what is going to be called out, so I don't have time to change, as a result I haven't got to play a 4 string live for a while.
My other group is Motown and disco, I wouldn't try that without a 5 string.