Well having both an ST and RS in my household I can comment on this one...

My dad owns a Focus ST and I own a Focus RS... To be honest I love when I get a chance to drive his ST... Its so much more of a nicer car to drive, far easier to live with everyday... Power is near enuf instant on it and its got a lot of poke (bluefin, decat and downpipe) and certainly can keep up with the big boys..

Would I swap my focus rs for it?

Would I fook... The RS is in a completely different league to the ST... The ST is a massive big heavy boat, the RS feels small, nimble and just eats up corners like you wouldnt believe... put a few right mods on and the RS comes a live... makes everyday driving an experience again and having driven quite a few cars in my short time in driving its good to have a car that excites you everytime you get in it!