Just to put a different spin on things, why not consider a faster platform, say X Trader through Velocity as opposed to J Trader which has been demonstrated to be 1/2 second slower. I don't know if this was mentioned, I didn't read the entire thread. I use X Trader and I am very happy with it and Velocity, it is lightening quick.
Also FTP, dedicated fiber to the home, is available in a few markets, with more to come, Qwest has it here in Denver, in a few places. Go cable over dsl always, it is faster, unless some weird anomoly. Good luck.
Additionally, if using cable modem, make sure you have a newer cable modem, I get faster speed now using a Motorola SB cable modem as compared to my outdated toshiba modem that was 4 years old. Apparently it can accept a faster speed, but don't quote me on that one.
Make sure you have the fastest computer you can afford with alot of RAM. Lastly, if you are big time, consider getting dedicated T-1 or 2 bonded T-1's, 1 T-1 may be sometimes slower than cable, but it is only your bandwidth and you get better service response should there be a outage.