If you really mean extreme cams, as pa-sjo says it will cost a fortune as solid (no shims on top) followers are needed, and even then not give too much except make it difficult to drive.

I've fitted Crower Stage 2 cams to a couple of Focus for people and the result was a better mid-range (the worse thing with 1.8s) and around 15 bhp on max power. As well as cams and pulleys, cost of fitting (including reshimming) and optimal set-up on a RR has to be allowed for.

Martin