Just about every record i do is in a different tuning. But the majority (although usually not consecutively) have been in drop C.
Usually i'll ask the guitarist to use a set of 11-52 dean markley nickel steels ( or d'addario) and replace the 52 with a .60...
If they really have a problem with the beefiness of the 60 i may have them try a 58 or 56 but i RARELY allow them to go lower. I've gotten in many arguments with guitarists about string gauge and how it relates to tuning and intonation, and luckily i usually win. Either they eventually trust me or spend an hour with me getting a doubled take in tune before realizing that we could have had the song done had they listened to me in the first place.
I usually up the strings a gauge or so as i go down. A B tuned guitar might see 11-64 or 12-64 depeding on what we are gonna be tracking (how much octave playing, lead work etc....)
If we go as low as A i may even use a .70 on the lows with 12s on the rest. Sometimes though i've used a .60 or .64 for A tuning. It really comes down to tuning issues.
D tuning usually sees 11-52 or 10-52.
Standard im ok with a set of 10s or regular 11s. I rarely allow 9s unless i really believe the player has the finesse to keep them in tune. And thats rare.
A good tip with low tunings is to tune your low string a few cents flat (between 5 and 10 or even more depending on the gauge). Have the guitarist play as hard as he possibly would on the tracking and hold out an open power chord and let it ring til it dies. If it stays in tune the whole time, your good. If not, the string is most likely going sharp becuase of how hard its been hit. Tune accordingly and REMEMBER where you tuned the string to on the tuner. Its vital for doubling and quadrupling takes and having a reference for bass.
Also dont be afraid to punch chords in by the beat or bar. I do it constantly, sometimes retuning for each new chord and quadrupling or doubling immediately. A pain in the ass yes, but prevents tuning meltdowns in the studio.
And I hate having one string with a much lower tension than the others.
