www.bobistheoilguy.com
This site is a great primer for knowing what makes oil work and what happens to it over time.

Want to do a little of your own testing? Here is a test you can perform without the expense of paying an independent lab. To compare the general flow rates of filters:

• Procure a set amount of amount of oil (i.e1 gal. We recommend a single viscosity. 30w works well at around 70 degrees F), the oil filter elements to be tested, a funnel, some sort of oil catch pan and some sort of timer with a second hand.

Note: To test spin on filters you will have to carefully cut the case off of the steel filter assembly to gain access to the filter core. You may also have to do a little work to hold the filter core assembly together with the outside case missing. Be sure not to disturb the element pleats or internal support tube so that you get a fairly accurate representation of what the filter element flows as manufactured.
• With the oil, the filter elements and any other items being used in the test all at the same room temperature, pour the oil through the 1st filter element and time how long it takes the entire amount to flow through filter element
• Repeat the process with the subsequent filter elements and compare results (of course you'll want to include one of our reusable oil filters in this test).