I spoke to a sales bod in my local T-Mobile store, and he claimed that all T-Mobile 3g masts should now be powered up for HSDPA.
Having said that, the guy was a prat (he dropped my
N95 on the floor, whilst taking it to compare it to his - which he obviously didn't drop!).
You can check your download speed in Opera, by downloading a file. The download manager will tell you the speed at which the file is downloading, and should be a fairly good indication of what speed you're actually getting.