i'm using a pair of 603's as well for overheards. they do an ok job. my room's not great, and some of the "cheaper" cymbals i have come across as harsh due to the freq bump the 603's have in the high end. their pattern is a little wide for my tastes, too.
i need to get a pair of mc-012's or a second B1, b/c i'd really like to give them a try.
although, i have to admit that since i got a new ride cymbal (K custom dark), i've liked the sound of the 603's more--they're a good contrast to the darker K. i've been replacing most of my cymbals with A's and K's for several years now, when the funds and stars align.
wade