I haven't done it for awhile, but I made some nice split card recordings. I always split the mics about 3', don't think I'd go for much more spacing than that as 3' gave a plenty spacious and defined soundstage. I ran split cards in places that would've been bad for cards in a typical DIN or ORTF pattern, like under the balcony at the Landmark in Richmond or at the back of DAR Constitution hall in DC.
I found it to be an excellent way of getting good recordings with good soundstage definition while helping eliminating room reverb, etc from bad sounding rooms/taping locations.
I haven't done any A-B card recordings in a few years since I've had hypers at my disposal, but now that I'm back to just cards and omnis, I might try it again.
Anyone have any experience with 4ch mic mixes with a center XY (or DIN) pair of cards mixed with a pair of A-B cards? I've tried that just once with my new Milab VM44 Links XY in the center and SP C4 cards split 3'. Came out good -- I liked that 4ch mix more than the straight XY card 2ch recording I made that night.