hakadate,
 Obviously everyone hates to pay a huge price premium and get nothing to show for it. I don't think anyone will guarantee me anything though.
 I used to connect at 33,600 here a few years ago using a USR WinModem (which I bought when the going price was about $150 and 56K did not exist.) I now use an external Zoom modem. (the lights tell me if the data is still flowing so I'm not always wondering if IE crashed, or a window is locked up, or what.) For the heck of it, I put the old WinModem in to see if it would go above 28800. No. The best I got was 26400. In other words, the phone lines have gotten worse, or at least the number I dial into is worse.
 Once every few months I'll connect at 14000 or so and wonder why everything is going super slow until I check the speed down in the windows "tray".
 However the connect speed is not everything. If I understand correctly, the later standards will renegotiate downward if errors are excessive, so your speed could go lower after you connect. I don't know if they ever go up. I sometimes wonder if modems are set up to connect at speeds they can't sustain just to keep the customer happy. Sometimes while downloading I can see by the modem lights that there are constant retries. When that is happening, it usually can be fixed by hanging up and redialing.