FWIW i opted for the 8Meg package with Sky and use a Netgear (54Mbps) router.
On desktop PC I see 6Meg regularly, on the laptop, it's around 1.5 - 2Meg.
Amyway, back on topic, with the above in mind, is pc connected wirelessly, the one you use most often and hence seems slow? As dougster says, it might just be heavy usage at the time you're on the 'puter.