There isnt any standard, and it would be hard to develope one......IM6,IM7, etc are a manufacturers trade names for the graphite they sell to rod manufacturers...the higher the number the more expensive, and its thinner and a bit stiffer so you can make a lighter rod..........Modulus...the higher the number the stiffer it is...but there are lots of other factors in the mix. Rod taper, type & amount of graphite in each part of the rod, type of scrim, component weight, guide spacing, etc.
A high IM number or modulus claim seems to be a good thing if you want a light, stiff, sensitive rod....or a lower IM or modulus might be better if you want a softer rod.....but there are too many factors at play to select a rod based on those factors alone. Cheers.