no matter who you are with, it all comes down the same phone line, and unless your I.S.P has capped your speed, they will all offer the same, and 4.5Mbs is good, if you are getting 450Kbs, then you need to test from your master socket test point with all extensions disconnected and see what speed you get there. if the speed there is much improved, then call your ISP and complain, BUT, make sure the wiring to the first socket is proper BT wiring, not a big DIY bodge, or BT will charge megga bucks for putting it right.