Drop D is often used for Blues based songs- Robert Johnson used it a great deal, ditto Elmore James- great slide guitar man, along with Duane Allman.. If you are tuned to EADBGE and you play all 6 strings in sequence, you have a 2 octave span and a E flat natural.. Just as I have way more than one Model 12, I have several acoustic 6 string guitars--Martin, Guild, Taylor and Gibson-- but my "workhorse" for Bluegrass is a vintage Martin HD-35, with fishman pickup. Kinda like a pre-1950 Model 12- 12 gauge 28" mod. solid rib--IMO anyway. RWTF