Sorg, if you want an idea of where probably 90% of all bands that use DRs set their amp's volume to record in the studio, do this: master output and channel output to 12o'clock, and gain at about 11:30-1o'clock depending on style.
THIS is a good volume to hear what a DR is all about. Even with 50 watts, this is screaming loud, earplugs are an absolute must here unless you don't value your hearing. Try and get some good ones with even frequency attenuation like a pair of re-usable and washable ones from Etymotic Research. At this volume you should be able to feel a decent amount of air flying off the speakers, especially with a 4x12.
Beyond this, you can go to higher wattages if you want, but keep in mind that at this volume, the speakers are already getting fucked (IE: they are breaking up, which is most often a good thing in small amounts). On my Road King (which is a DR at heart, it just has way more channels, etc), if I'm feeling adventurous, I will set all 6 power tubes up, and then set the volumes like mentioned above.
All I gotta say is: :shock:
This is where **** starts vibrating off walls and cups on your desk start doin' the walk. lol