I think that would be a best-case scenario for you.  Assuming a 40% increase every 14 days, you are looking at almost twice that by early November.

15-Aug    50,000,000
29-Aug    70,000,000
12-Sep    98,000,000
26-Sep    137,200,000
10-Oct    192,080,000
24-Oct    268,912,000
7-Nov    376,476,800

Keep in mind, that it will probably increase more than 40% with all of the hashing power that BitFury, HashFast, KNC, ASIC Miner, CoinTerra, TerraHash, and BFL will be releasing between now and November.

I wouldn't be surprised if it's over 400M by November.

Cancel your order and buy some Bitcoins if you want to invest.  That 50GH/s is going to probably net you about $5/day by the time you get it.