Try the TDCi 115 - Group 6 insurance (Zetec version), excellent mpg and the torque is superb!
They do a TDCi Sport now - 115bhp and has exactly the same spec as an ST170 (seats. fogs, wheels etc) except the engine

. As an ST170 owner i reckon this would out pull my car between 50-80mph, and chipping these things see good results.
Heres fords info..
http://www.ford.co.uk/ie/focus/foc_e...isport/-/-/-/-
Sure you could get one cheaper than that though