You might want to check Consumer Reports online. I don't know if they have reviewed the model you're looking at but, IIRC, the Dyson they did review didn't perform particularly better than the other models.

For $20 or whatever they charge for their online access, it is money well spent, IMO:

http://www.consumerreports.org

Of course, they probably wouldn't recommend you get an X5 either... but I'd trust them for for home appliances