You'll get much the same FTTC product from any ISP at your exchange. The FTTC is provided by BT Openreach. Beyond that it's down to the ISP's backhaul network, but the estimates are only of your sync speed to exchange.
All ISP's get their estimates from the inaccurate BTw database which often underestimates. It's only an estimate after all.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC