Hiya
The main problem with upgrading is the fact that on the whole you will not see a heap lot of difference. This is because MOST sites you visit or download from are limited to the speed you can draw info from them. Some are choked at 256K. So you MAY be able to download from 4 sites at once but in my experience this is a rare occurance. I personally would stick to the umlimited version.
Cheers
Mike