Lowest commissions for 5K-15K shares?

I see many speak about IB and their low commissions. That seems to be the case if you buy 100's of shares, but does not appear to be the case when buying thousands, particularly 5k-15k shares.

My guess is a broker with fixed pricing would be best for these large trades: Fidelity, ScotTrade, TDA, etc.

Please share your thoughts and experiences. Thank you for your time.

 

In addition to commissions, you have to consider the quality of the execution. Does the broker get the best price? How often is there price improvement? Each broker has some data on this hidden somewhere on their web site. It's difficult to compare but it's something to consider and a reason some are willing to pay higher commissions for large orders versus a $5 or $10 flat rate.

 

Great point hurricane and I understand. This will be considered.

 

Also keep in mind that ( given volume ) you can "negotiate" the advertised flat-rates even lower with the likes of Ameritrade and others.