http://elcova.com/groupee/forums?a=search&reqWords=K%26N
Search reslut for K&N
K&N Search Result
Search Reslut for Volant
volant
So yes there is plenty of info on the subject.
To answer your question. In my opinion Volant is the way to go although it is one of the most expensive systems. The main reason I like it or went with it is that it is sealed unlike the K&N which exposes the filter to anything that has access to the engine compartment (excess dirt and debris) You will feel an improvement after the install.