average spread between interbank rate and various brokers

Does anyone track this? Is there a way to get this? Basically, the mean, median, standard deviation, etc of the spread between the interbank rate and the various brokers, eg: oanda, fxcm, your favorite online broker here.

If we could see this, we might get a sense of how much we're trading against the market at large and how much we're just trading amongst ourselves as speculators.

If you think that their is a difference with interbank rates to brokers then there is a problem?

Don't mean to be harsh, just that observing what I think is a quality ECN to various banks like EFXgroup, I don't have to worry about getting gipped, I can bid down to a tenth of a pip in between the spread. I see zero pip spreads regularly and low spreads for GBP crosses for around 4 pips or less.
I guess Interactive Brokers are an ECN also, but my question about their less than clear web site for forex nuts went unanswered and my question to EFXgroup did get answered, though I'm not a client there yet.

Along these lines, I don't understand why DBfx has fixed spreads, though they have the capacity to be very competitive, they choose to have some bigger spreads than EFXgroup. Low spreads with commissions and customer service that gives a rip will separate the giants from the has been, you think!!!

Well, for some trading systems I'm sure it's not a problem. For others, it might be.