This isn't really an answer, partly because the question isn't answerable as asked. So, what do you mean? Mixing acetone and water in various proportions can give "good results" for many things depending on what you are trying to achieve.

Sounds like you are screening for an optimal soloubility of a reagent in a mixture of water and acetone?

Maybe you want to have a look at the Log(P) value of your reagent:

http://en.wikipedia.org/wiki/Partition_coefficient#Pharmacology

chemspider is able to estimate these values:

http://www.chemspider.com/Chemical-Structure.236.html?rid=e5bd8e1b-c45a-4152-bc67-6ed13b840861#acdLabsTab

perhaps you can find some correlation to this descriptor.