If you are sitting on ISLD waiting 2 mins for a fill, then it is because the market has moved away from you, not because of a slow broker. How exactly would a discretionary routing algorithm preference an ECN on which it can see no quotes? One way I can think of is that it could send an IOC to ISLD then send the rest elsewhere. If that's what they do, and if you didn't immediately fill on ISLD, it is because the spread is not there for you.
I trade QQQ almost exclusively (although not your 10K-20K per lot), and as far as I can tell, ISLD is still the best source of QQQ liquidity. I almost always get price improvement over what I see on ARCA. If I want in (or out) with an instant fill, the best way seems to be a sweep of ISLD by a few cents outside. But you're right, the spreads are not nearly as tight as they used to be (talking pennies here) and I'm considering moving over to NQ for that reason.
Last time I checked, ISLD traded twice as many QQQ shares as INCA with ARCA a distant third (approx half of INCA). AMEX still sux bigtime, and if there is even a *chance* that my market order may get autorouted there, I would not send a 5-figure order to Intelligent. I say again, sending to Intelligent on TS (especially with your size) is baaaaaad news.
My primary broker is TS, but I also have a second account at IB with similar experiences there...
--Derek
