Just for interest sakes in case someone brings it up in the future again. I thought I was going crazy or something but the speeds have really increased quite drastically and I will explain why. As I stated, I was using the Nokia 6680 as a modem, with the phone on Dual mode thereby covered by the 3G network.
To connect I was using the Vodaphone "Dashboard" program supplied with the Vodaphone E620 card, with the phone as an "other modem" within this program, so that I could track data usage per session etc.
It turns out that this program was not allowing the 3g network but only gprs /edge, even though the phone was set on 3G. I discovered this when I used the Nokia connect program within the Nokia PC suite and set the connection to MTN. The PC suite automatically set the APN to myMTN, which was the reason for my previous question.
After a bit of testing and speed tests etc under the various programs, I discovered the difference was not the APN but indeed the program used to connect to the net.
As I said, just something that i am putting out there in case someone does have the same situation in the future, which may happen because of the MNP and people having the connection programs of other networks until they can get the MTN one etc.