generally if i'm off-center i'll go XY. if you're not in or even close to the audible center(stereo or mono mix), it's really not worth running a stereo config. IMO. HOWEVER ........
many people have noted on this site that they really enjoy the off-axis sound they get with the akgs(both the 39x and 48x series, or the mic of their choice for that matter) when running near-coincident patterns like DIN , DINA , ORTF, NOS, etc. i've read that tapers generally prefer DIN or DINA with the akg's. no personal experience just what i have read here.
if you are far away from the sound source the XY config really helps "focus" in on the source IMO especially with hypercardioids. although it rolls off the bass naturally, it makes it sound a little more "upfront" and the bass is a little more focused and less boomy. like i said though lots akg users enjoy the off axis sound with near coincident techniques. I'm not sure if allman's runs a stereo mix or not so it's really kind of a crapshoot. especially in a shed where there are so many different variables when you are not in the audible center.
flip a coin or listen to somebody who has taped there before from far away and off center. with solid mics like the 390s you probably won't make a bad tape no matter what config you run
whoa did i just fluff akg's
good luck! let us know what you decided to do and how turned out!