If using to monitor then you can get by with just the EGT as it tracks mixture closely. But it can also be an indicator of other problems and not just fuel. They really give best and most useful info when used together along with a log of other sensors. I feel a good wide band is essential if tuning as is an EGT, as it will also show when timing is happy, and an 11:1 A/F should never cause problems with detonation unless unusually hi compression pistons or rediculous amounts of timing are used.

What do you want the guage(s) for tuning or warning?
Rod