No they dont have as much gain as an 81, but its pretty close. MORE than enough gain for lamb of god (who dont really play with all that much gain anyway: its a fair bit, but its not silly levels)
The pig is much heavier and thicker than the 81. And it still has similar clarity and tightness.
Warpig and 81 cleans are not even comparable. The pig is a whole different ball park: its cleans arent "Good for a metal pickup", as you often hear about high gain pups, they're GOOD. End of. They might be "OK for a bare knuckle", but they're much batter than many lower output pickups that have a good reputation for clean (*chough* JB).
I think the pig would be perfect for you. Hell, you'd probably really like a miracle man, and thats supposed to have the worst BK clean (its still quite passable)