Cats, what sort of gains to expect??

Well i had a wee play with my mate Rich in his R32 tonight, he has just had a milltek res exh and cats fitted, std map and airbox at the moment, and i have a Revo stg1 and milltek non res exh on mine, he pulled away in 3rd which surprised me, so are the cats responsible or is it just my car being a gay sow ass 5 door?? If the gain is as much as i think i will be ordering some cats soon