There is long range middle size aircraft in the market - Boeing B767-200/-300. But Cathay Pacific refused to intorduce any models of B767 simply because there is no Rolls Royce engine option on B767 other than -300 variant (not even -300ER ones), and Cathay Pacific uses only aircarfts with Rolls Royce engines other than A340-300 (because Cathay Pacific uses only 4-engined aircrafts on long haul routes for maximum passenger safety).
What a large mistake for Boeing and Rolls Royce not offering Rolls Royce engine option on all variants of B767! If there is Rolls Royce engine option on all variants of B767, then Cathay Pacific must be running B767 long long ago, since its launch in early 1980's!