You just need to make sure you're using 3g to actually test your speed.
Also, what's your definition of "embarrasingly slow", as this could vary widely.
There's no difference between using either the wap.o2.co.uk or mobile.o2.co.uk access points, and you should be able to use any of the o2web, vertigo, or bypass usernames with either of them, all with the password password.