Halfords usually have multiple sources/amplifiers/speakers on their display stand controlled from a switch panel, I think I should take a CD along with me and audition their warez sometime.

And when you have finished doing that, you will have a really good idea of which speakers sound the best in that small audition room, being driven by Halfords' choice of amplifier, from which you will be able to derive practically no useful information about how they will sound in your car.

Reading the specs on the speakers (as macrzool suggests) is actually more useful than listening to them in an environment totally different from where you plan to use them.

tanstaafl.