Much faster yes
I got one for my laptop from Three, who I already had a phone with and so got half price line rental.
The 7Mb/s speed is apparently not in place yet, but is rolling out later this year. So currently I'm on the 4.2Mb/s which is pretty fast for transfers yes, but does suffer from latency. Normally it's only 200ms or so, which is fine for light gaming and web browsing, but not if you have anything to do which requires rapid reactions (I'm guessing work wise it's not an issue) then you might have trouble.
I've noticed that retreiving web pages is quite slow on inital conection to a server, or after prolonged inactivity, but that file transfers and torrents can easily reach 200KB/s, which I find pretty respectable for a mobile device. There's also the added bonus that these HSDPA modems seem to be pretty Linux friendly.
If you do a lot of data downloads, yes this will help a lot, but be careful as the upstream seems to be pretty limited, I've never passed 40KB/s on it. Otherwise, I'd stick to 56k