Wondering how people determine daily track 'variants'???

I have used speed ratings quite a bit, however they are very time consuming and I wasn't clear on the best way to establish a daily track variant???

Would you take all times ran that day by winners and avg them to find a variant??

Some dead track times are as fast as good tracks, even some slow track times appear to be run on good tracks?????

I had problems making these adjustments????
Speed raters out there? How do you work out variants??? Do you ignore tracks worse than dead??

How do you take into a/c wind factors also??