Having run MK5 in omni mode alongside MK4Vs, I continue to be of the belief that for stereo recording at a distance (such as at a music festival), omnis are an inferior option. Meaning, maybe the CCM5 makes the most sense -- you get the nice HF bump, and you can run omnis in a pinch or in whatever other situations (up very close) they might be preferable. I wouldn't delve into a completely different mic system just to have a CYA option.
Wisdom there in the last bit, unless it's a CYA thing for rainy days when it might make more sense to leave the costly and delicate stuff safely packed.
As for the first bit, I've found that when recording outdoors at at festivals, omnis + a cardioid or supercardioid (or two, or three or four) is better than a single pair of either omnis or cards by their lonesome.
However, I fully realize that's a more complicated setup than what many tapers are interested in.
Recordings made at a distance using omnis alone often benefit greatly from a presence-range EQ boost. Whether or not a high top-end boost is also needed depends somewhat more on the response of the microphone and the PA mix.
There are some mighty fine sounding examples of good omni recordings in this thread!