Well it depends on at what bit rate you will be streaming also as that will define the maximum # of connections your bandwidth limit can take.
i.e if it is for example say at 200kbps, than with server one you will be able to provide streaming to up to 150 users, and a single server can handle 300 concurrent connections.
but if it is like say, at 20kbps, than on a single server you are looking to have 1500 users at max. Where server hardware might start to breakdown. In that situation being on 2 servers will be better option.
So tell us what exactly you will be streaming first of all. Video or audio. And what will be streaming bit rate, and expected no. of connections during the peek!
since you are already using more than 20mbps, you need to have more bandwidth as your first priority. Hence out of the given 2 options, you have to stick with the first one which has 30mbps bw, as other 2 will just add up to same as now of 20mbps, while your needs are more than that.