Please your full router stats for ADSL-GMT & we can tell if it'll be faster. It often is.
Also what does BT Broadband Availability Checker estimate for your phone number? Post just the whole table and the line above it, blanking out your phone number. If it doesn't recognise your phone number, use the Address Checker, not the Postcode Checker.
Looks like ADSL2+ would be better for you but the BT Checker is only an estimate often lagging behind reality. Your full router stats would provide a far more accurate indication if you would post them.
I'm not familiar with HHs but you could try 1 of them around http://www.kitz.co.uk/adsl/frogstats.php#72 .