Pro and Cons of E85

Here is another question.
Is there enough gas in E85 to still read a spark plug, or is that one more thing to add to the E85 conversion?(02 sensor in the headers and a gauge to read it!)

If you have a good-quality, working, A/F meter, is there any reason why you should need (or, want) to "read" spark plugs? I'd think the mixture information you could get from a wideband, data-logging, oxygen sensor would be better than anything a spark plug could show you, but I am asking because I don't know. :banghead: