Even for a wild guess I think you're off by at least an order of magnitude if you don't take into account velocity (typical dollar is spent four times per year; edit: and bitcoin, as a digital currency, is likely to have higher velocity) and the different types of money (monetary base is maybe one fifth of total money supply).
Note also that your math involves 12m BTC but your page says 10m.
I may very well be off by a factor of 10. Agreed. But what is your estimate? and what exactly would M2,M3 and M4 be?
Let's assume 12m has been mined, 1m has been lost forever, 8m are hoarded, and a velocity of 10. You then have 30m bitcoins in transactions but 3m bitcoins circulating. In this case my estimate is off by a factor of 2 - 2.5 (but it could be 10, sure). But What if it doesn't take over half of paypal's transactions, but rather 4 times all of paypal's transactions? That's why I think any estimate is pretty hopeless. A good order of magnitude is ... if it reaches paypal scale it will be in the thousands.
Since there is no fractional reserve banking (yet, anyway) in the bitcoin economy, I don't see how the monetary base can be 1/5th of the money supply (but I might be missing something).
Note also that your math involves 12m BTC but your page says 10m.