As to when they are getting more servers, you might want to email fastservers.net directly, they probably know the answer better.
There are some subtle differences to the mega bits and giga bytes issues here.
To say that you get 1mb/sec burstable bandwidth, it means that if your traffic is pretty high, you can transmit up to 1mbits of files per sec (or roughly 1,024kilobits/8+1 bits = 113 kilobytes per sec).
300gb actual is the maximum amount of bandwidth your site can transfer during a given month but if it is not capped, you might be able to burst at higher transfer rates then suddenly slow do to almost zero.
You have 86,400 seconds a day x 30 days x 113 kilobytes, you get about 292gb or roughly 300gb. Okay, it is probably the same. My computation is a little out but you get the picture.
So basically, it is two ways of calculating the same thing. Supposed if you want to get from point A to point B, you could say that if you drive at x miles/hour for a month, you get there or to say that from point A to point B, it is x miles. Same thing.
The first may signify a constant speed while the second may be one which can be erradict.
In the point of the bandwidth, you could consume 290gb in a day and then for the rest of the month you have no traffic and then the last day 10gb.