if I tune my guitar to Eb, Ab, Db, Gb, Bb, Eb, the strings feel the same, a little easlier to bend but the same.
if I drop the E, to D then of course it goes a little loser but the feel of the string doesn't change, dropping it to C is acceptable, re-reading I'm assuming the orignial poster is about keeping the same tension but with the dropped tuning.