if you're trying to host on a 300kbps upstream link compared to a 12mb one, then i think you would notice the difference. because my moves can get to the server quicker on the quicker upstream, it means my downstream time is much more responsive.
The OP isn't on about hosting though are they, of course more upload bandwidth comes in handy when hosting but for ping times in general, be it 512k or an 80 Meg connection, the ping would be the same.
ping times can (but not always) be better depending on what type of product you're on. but say for instance on an adsl connection, you're getting so many crc errors they are degrading the performance of the line whereas on vdsl there are not soo mant crc's that it can improve the quality of your line. boom.
Well so far I'm very pleased with the quality of my infinaty line everything has improved in terms of quality I have almost zero jitter when I test my line (most tests return no jitter ) and a much much lower ping than on adsl .although I had 13/14meg on adsl I still found it difficult to stream iplayer and such on the ps3/laptop .now though even when all the kids are online I have no problems with hd streaming everything is seamless .only quibble is the dam OR modem and router my Internet will cut out one a day .all lights are green but no conection !a quick restart and all is back to normal .think there is a detonate problem with bt equipment as this problem seems very wide spread and I had never had one single problem with cut outs prior with bt adsl bb.but shall be getting a good modem router in a few weeks as I'm sure it's the bt supplied gear that causes these problems ..