It really does depend on the quality of the camera and the monitor. I've had some monitors be of little help, either washing out, or being incredibly blurry, others fairly good. I haven't ever noticed a lag. I also have mixed feelings on infrared cameras. For the most part I love them, being able to see blackouts, etc, but they have a tendency to switch to infrared at inopportune times, especially if you happen to have a DISCO BALL in your show. That was a pain.
If you have lots of tech available (which is rare), it's great to have several channel choices, so you could have a closeup on something you specifically need, on channel 2, or a shot of the conductor for a musical, etc.
Erin