Serious question, for a second:

Does anybody know how much of Bitfinex' volume (on average) is routed to Bitstamp?

Bitstamp's API returns total volume (i.e. their own volume + orders from Bitfinex). Bitfinex' API doesn't distinguish between orders executed "internally" and "externally" either, to my knowledge.

The result is, we can't say for sure how much of the volume on stamp on finex is a duplicate... Can anyone who trades a lot on finex shine some light on this? Maybe you know how much, approximately, is routed to stamp, so we can at least guess how much stamp's volume has to be discounted.