hopefully nothing. this won't make your site faster if you're not using more bandwidth than can be used with 1mbps. 5 mbps over 1 mbps will allow you more bandwidth. 1 mbps is not very much - figure the best you can squeeze out of it is 280 per month, and probably not that before you overload it and things slow down. 5 mbps will allow you over 1000 gig of bandwidth per month.

just remember to check out your potential host and server - a host who is down a lot won't make you more money and a lesser server could also mess you up.