Broadband Speeds

I am presently on a Sky Unlimited Broadband package offering a speed range of 11.2Mbps - 18Mbps. On checking with BT they can offer a speed range of 6.5Mbps to 8Mbps. Are the different speeds down to the equipment used or if I did change to BT for Broadband could I expect the same speed as I have with Sky?

Regards

Tom