It's not how low you can tune, it's how you play your instrument. With that said, a low tuning can enrich an already heavy song, but that's it. Black fucking Sabbath, people.
Well i tuned into D cause i did covers that are in D tuning, so i began composing this way so i don't keep tuning up and down.. and kinda liked this tuning.... but a fellow guitarist squirmed at my tunings..i'll understand if he is tuned in E but he mentioned around B or C. He wanted to join my band as a 2nd guitarist w/ a condition that i change my tunings.. i just said u play at your tunings and i'll play w/ mine.. we'l work it out he he
Any tuning can sound heavy, its all depends on the user(s). having said that tuning down will make you sound heavier, but that won't make it good. in fact I find down tuning makes it easy to sound generic, creativity is still the ultimate tool.