The downstream speed seems good, residential broadband is usually download-oriented, and they usually discourage customers from running any server applications, hence the disparity.
I'd try the TCP Optimizer's "optimal" settings, what OS are you using ?
I am running mac osx 10.6.7
I also have a pc which I think runs windows Vesta.
Well, you are on a node. If others are using a substantial amount of bandwidth you are going to slow down a bit.