I LOVE split omni's. I would never go 3:1 though. The widest I have gone was a 15' split and that was about 100' back. Here is a pretty good example of that
http://www.archive.org/details/ddbb2005-05-28.mbho.flac16 . The soundstage is quite wide at a 15' split, and I actually like it but I don't think I would want to go any wider. This was part of an 8 track multi/matrix but ddbb said no to posting the matrix. The other recordings from the fest used the omni's in conjunction with board and 2 other pairs of mics on stage. It was a nice treat being able to manipulate the image and kind of layer the soundstage. I LOVE split omni's outdoors either alone or in a matrix.
I have also used splits many times on stage. The thing with stage placement of any config is you can get too much of some of the instruments and not enough of others. When there are vocals don't bother, but for amplified jazz it is the shit IMO. I did a 3 night series of Fareed Haque group last year and the first 2 nights I ran mono board + stage corner omni's + center-stage x/y. The Tabla's player was set up center stage so I got way too much of him the first 2 nights. It was a tight club and I didn't have a lot of option. The third night was at a small outdoor stage and I ran split omni's at the lip and an ORTF pair from the audience. That recording was much better. I had a chance to listen to the other two from previous nights and noticed I was light on a few of the instruments, so I place the splits a little closer to instruments that I felt were light from previous nights and away from the tablas player! When just going split on stage I usualy try to stay around 6-8 ft spread and just position the mics so I am away from direct sound sources. Also, if possible I like to be centered on the drumset because I like to hear the placement of each cymbal and drum. I guess the key to a good split omni stage recording IMHO is to think of each mic individually for what it will record, and try not to split them so far as to create that hole in the middle. I would never go 15' spread on stage, but 6-10 is probably just fine depending on the spread and depth of the stage.
I recorded fhg again a few months later and they set up after the opener. Knowing the blunder I had made on the first two by using x/y I set up splits. Turned out that the keyboard player wasn't there that night and the tablas player set up off to the side and was again to heavy in my mix! Another nice perk of recording split omni's over a card/hyper config is that you get a little more crowd responce. For a wild rock show this is not an advantage, but for an instrumental show this is often a big plus. Getting crowd at appropriate times without a lot of room-boom is a nice thing to my ears.
As for being too close, I once forgot to change the caps to cards for an x/y recording and did x/y omni's. Surprisingly enough it was not a bad image! It was far from what I got with splits but certainly not mono. I recorded a multi/matrix using onstage x/y omni for the opener, and then split omni's for the headliner. I can pull out just the mic tracks and do a comp if I can find the time in the next couple of days. I think people here will be surprised. I know I was. That effor was with Brian Ska, and MattD at the Metro in Chicago for Goran Ivanovic Group and Andreas Kapsalis Trio. Goran got the splits. Actually my current avitar is from that show.
Matt