Lower output pickups have less compression, and therefore the high gain tones tend towards crunch rather than the more saturated sound you'll have heard from the warpig.
Conversely, higher output pickups have more compression, and the clean tones have less 'bloom' as a result.
The black dog can get heavy, but for pure nastiness on the heavy tones, I personally prefer a higher output pickup. BUT, the cleans on the lower output pickups are stunningly good.
Mules will give you great clean tones and great rock tones, but when it comes to metal and harder tones, I don't think they'll sound great. They won't sound bad, mind, just not great.
There is no perfect all-rounder, but there are pickups which can do several things exceedingly well. You have to decide what is most important to you!
My impression from your post is that you're not after the broooootalz. The other main application for the warpig would be stoner/doom, but it is also used a little in some bluesy applications too, I understand. But for pure blues tones, the mules are a far, far, far safer bet!