i get 42 on normal motorway drives and at one point ive had 47 but just kinda depends if youve had anything done to the car, ive got a different exhaust on mine so ive lost the two big centre cats and a k and n filter which really do help even driving at 75 in 6th is doable.
head gasket would be a good check on that age of car and depending on miles as they are quite prone to go
mines actually up for sale on ebay at the moment