I have 904s and 604s, The 904 is more rugged and sounds a bit better in my opinion. We shot out Audix D2, Shure Beta 56, Heil PR28 and the Sennheiser. They all were good sounding mics and worked, the Sennheiser was the most user friendly of the bunch, and we've been happy. I will probably add some of the new Shure Beta98AMP next year, I am pleased with their performance too. I've tried the Beyer Opus series and like them too, but I have had some issues with Beyer service.
On a side note, the show I am mixing tonight we are using 421s on the toms, the drummer wanted them but is complaining because he can't get his cymbals as tight as he wants them. He was the reason for the 904s. Although the 421s are great and the tone of the drums carries through nicely, I am missing the punch I seem to get from the 904s, we are getting ready to A?B them right now.