After some delays I have some more news on this issue and potentially a solution which I will be sure of later.
I had a lot of success using the USR card with VOIP, but I have not found the cause of the much lower bandwidth. I did try disabling miniPCI and wireless in the CMOS, but this didn't seem to fix it. Strangely, I got very mixed results on different internet speed tests - the BT speedtest reported my USR card as similar bandwidth to the on board card. However several other speed tests reported it as much slower, and as said before I can see quite a lot of packet loss.
BUT - yesterday I went back to the on board network card. I tried to install the latest drivers from Dell, but the driver claimed that it was not compatible. Then, I tried one thing that I had not done before
- in the device manager wireless card options I disabled a number of options that I felt were not needed - e.g. Bluetooth sharing, anything to do with 802.11b, and automatic wake up support for network card when in standby(these are options that can only be accessed from device manager and not from the wireless card program). Eureka - the one minute timed second long glitches seem to have disappeared. I will try this out with real world VOIP later on today to confirm.
cheers