I used to have an ST with a Pumabuild remap - basically a mountune map with a bit more mid range boost
You lose some of the 5pot warble when you remap them though
They are great cars, great seats, handle well, the sound is amazing - pops and bangs through standard exhaust
Mine was about 6mpg worse than my GTI - if that bothers you??
The ST3 is the one to go for with leather seats, heated front screen (AMAZING feature) and 6CD changer
The downside though is the weak engines which have been known to crack the cylinder liners on tuned (and even some stock) engines. Jamsport have released a block strengthening kit for about £1k which solves this.
Alternators, driveshafts & Oil breather diagphrams have been known to fail
You will need an uprated clutch with a remap, mine slipped straight after the map. The Focus RS one will fit the bill £700