Speed Gordon is a fictitious man used as something to emphasise the incredulousness of a circumstance.
e.g to a person who has a lot of shoes, you would say "geez, you've got more shoes than Speed Gordon!" therefore, it is assumed that Speed Gordon has many many pairs of shoes, but you - amazingly - have more.
e.g when a person smells quite badly, one might say "Jeff smells worse than Speed Gordon!" again, it is assumed that Speed Gordon's odour is extremely offensive, but Jeff smells worse.