Time it takes for BFL to produce and ship 300 500GH/s rigs = 10 months to indefinite
Time it takes for BFL to finish current order chain = 10 months to indefinite
Hashpower increase once order chain is finished = Way more than 300 TH/s
Also, BFL has said that they won't sell enough hardware to 51% attack
So money required to create roughly 50 identities to purchase the 300 500Gh/s rigs? Millions of dollars.
Was just using the pricing from BFL as an example. Obviously you wouldn't be ordering from them. You could very quickly build custom hardware here in China for far less money.