I'm trying to find out which acoustic guitars handle detuning a whole step or even drop C (C G C F A D) the best. I can't seem to find any commentary or websites that discuss this.
The longer the scale, the higher the tension. The higher the tension, the less floppy the strings will get in dropped tunings.
You can't go wrong with a big body and heavy strings. Jumbos and dreadnoughts come to mind.
I keep my Taylor 110 tuned down a whole step and it works just fine. I also detune my 12 string down by a whole step to reduce tension, and that sounds fine too, but there was a point when it used to be in Open C (C G C G C E) and it still sounded fine and never experienced buzz. The Taylor can also go as low as (B G C F A C) without buzzing as well or without losing intonation.
I would imagine that the scale length would be all that matters really. If you're using a 25.5 (right?) scale length, (used on most guitars) then that plus a heavier string gauge should be all you need.
Any an all acoustic guitars will be fine for the job. You just need to make sure it's setup properly to be able to take the tunings.
my husband keeps all his guitars tuned down including his j-45, which is a short scale, and they all play great. btw, he's kept them all turned down for years with no issues.