While you may be very high DPS due to tanks generally being strong with vengeance right now, your main job as blood is to tank, so DRW should generally be used when you need the avoidance. Of course if it's trivial content or you're trying to rank for DPS as a tank then sure, save it for soul reaper.
and of course if the stars align and you get a low health enrage it makes sense to use SR to burn blood runes and with higher damage using DRW is always a choice, just keep in mind the heavy RP cost of it, especially if BT is your T75 choice
Here's some of my thoughts on DRW usage from another thread.
Originally Posted by burbon
With regard to DRW, depending on the progression of your guild, tank dps actually matters now. DRW is the single best tank dps CD in the game. Obviously it's primarily thought of as an avoidance CD, but you should still use this as many times as you can in a given encounter.
Just use your best judgement and if possible stagger using it for specific mechanics as they may apply, but if you're waiting to use it for when you get trucked, you might find yourself using this only once a fight, and that's a huge waste of dps considering it's on such a short CD. Between things like ghoul sack and lichborne, both of which are on 2 min CDS, we have more than enough emergency CDS and this is one that I prefer to use more for dps than for survivability.
To elaborate a bit more on this, 20% avoidance is nothing to scoff at but it's RNG. All of our other CDs have predictable and quantifiable value. The only reliable thing about DRW is the boost in damage and while it's a great survivability CD, I opt to use it as often as I can for dps, considering how well DKs are doing right now with survivability.
To put it another way, it is unlikely DRW will prevent a tank death in the same way that IBF, lichborne, ghoul sac, purgatory, or ERW popping several DSs to heal you quickly would, but it will assuredly lead to faster kills if used more often and in conjunction with execute phases.
for 5 man heroics, which are a joke, i think you should... no questions... i'd say 90% of the time i'm #1 on dps on 5mans. i usually pop drw, ub (not sure if ub gets copied), ghoul and cycle mobs and sr each one that's close to 35%. depending on vengeance, seeing 200+k hits isn't unusual.
dont wait until 35%, try to time it so when the 5 seconds are up the mob is under 35% so you can maximize applications.
for raiding it's more situational. i often find myself using it right after a huge hit that takes me below 30% along with other cd's to get my health back up (maybe vamp blood and/or death pact). this helps with additional hits hopefully not killing me along with a huge dps increase when combined with other cd's like ub, which hits pretty hard.
If the Boss is at 35% and DRW is available, I don't see why not. Very few bosses thus far have anything parriable other then melee swings. So you really ought to be DRWing on CD anyways to boost tank DPS.