There was a thread here about a month or two ago relating to
oil filters. A real good apples to apples comparison. But it did mention the filters all had an internal bipass when the element gets clogged with debris. So the
oil only gets "filtered" until the filter clogs. Then it just recirculates back through the engine without any filtration at all. The study actually raised more questions than it answered as to which filter is the best. But it's worth reading. I think changing
oil every 3000 miles benefits the oil companies more than the car owners. But in a Cobra that could be a couple years.