I'm personally of the opinion that if you're good enough for an IB to be interested in taking you from a prop firm (rare and unlikely as that is), you'd be better off staying where you are. They're two totally different careers, one isn't a stepping stone to the other...I think a lot of people have a massively over-inflated idea of the glamour and excitement of trading at a bank; no offence to Gooseman/GJ etc., I just know a few boys who are/were involved in that line of work, and the consensus among some is that it aint quite all it's cracked up to be. That said, a lot of people love it more than their own mother.
With regard to the OP, based on what I've read from you here I'd be less worried about whether it's prop or IB for you, and more worried about whether it's trading or a seat with the BNP..