Studio Projects website claims that Max SPL is little higher for C1, and frequency response seems a little flatter judging by polar plot. That said, I thought they were basically the same mics except the C3 was multipattern. Anyone else fill in the details?

I may be going out on a limb here, but I still would consider getting 2 mics for stereo recording of the acoustic guitar. I guess it depends on the style of music and your taste. Good luck on your hunt.

My favorite trick for recording a singing guitar player is to use a figure-8 mic on vocals. Point the dead plane at the sound hole of the guitar - gives you great isolation on the vocals. If the room is less than ideal, I have a couple of small baffles - I'll stick one a couple inches from the back of the vocal mic.

I have also used a figure-8 on the guitar - point the dead plane of that mic at the singers "sound hole". I'm trying to get guitars recorded in stereo now, and I don't have the necessary mics to do that with all figure-8s - I'm getting close though.

One more CK94 capsule and I'll try recording guitars Blumlein with a baffle on the back side (if necessary).

Back when I was buying my first Studio Projects C3 mic, I was wondering if I should get 1 or 2 multipattern mics - I couldn't see much value in the Figure-8 pattern, besides using it for MS stuff.

Figure-8 is now one of my favorite tricks. It's a very powerful weapon in lots of different circumstances.