I think the thing with on-stage omnis needs to clarified a bit...
at least this is what my experiments tell me...
The term "on stage" might be used a bit too loosely...not all staging situations are alike...
For small rooms - where the band might have their back to the wall or their amps near the wall - omnis tend to sound like a complete mess...everything sounds too flattened out, response-wise...and the spatial effect is not what you would hope for...
But if the band is on bigger stage...where there might be 10-20 feet of open air behind the band...then omnis make nice recording from the stage.
For the small rooms I've been using cards - attached to each guitar players vocal mic stand - about 30 inches from the ground. L-R - various spacings...as much as 20 feet, as few as 6...aim the mics between the guitar amp and the drummer - my mics generally end up 5-7 feet from the nearest guitar or drum. I try to avoid the bass amp - as thats the most likely path to brickwalling...The cards produce a very tight discrete sound.
Add the board mix - I record both sources as loud as possible...In my case the board has only vox, kick and sometimes overhead...this makes the vocals sound very clear..but you still have the nice onstage sound...
Here's a recent matrix...perhaps a bit hot out of the shoot...
http://www.archive.org/audio/etree-details-db.php?id=22735&from=browseRecent