There's many variables involved bob, the 'up to 50' part will be the maximum throughput of your circuit not taking into account your distance from the cabinet (FTTC), contention on service (likely to be around 1:20 or more), and actual throughput possible on the router/firewall (enabling DPI/IPS can half the maximum throughput of your router although this is mainly SMB/enterprise appliances this applies to).
FTTC would normally be up to 38Mbps or up to 76Mbps. FTTP has at least 12 options for speed as its really dictated by the carrier and to be honest I know little about cable as Cornwall has no cable options, but I suspect you are referring to a cable connection?
For reference, I've got 'up to 76' and frequently see around 45mbps downstream with around 11mbps upstream.