I love to run split omnis.
On-stage, or stage lip is great, but you have to watch out for monitors. They can throw off the mix and image if you are too close. I try to keep the mics centered on the band, but you have to keep your distance from drum kits and amps. I usually spread them around 6ft, never gone less than 3ft.
Once went as wide as around 15ft for a couple JMP shows, but the way the band was set up allowed for it.
JAson