Metro, I can't point you to anything specific with regards to warranties but I can point out some facts of life.
An oiled cotton gauze filter (OCG), and K&N is only one manufacturer of them, is at the low end of the efficiency scale amongst the available filters, both OEM and aftermarket (excluding offshore, noname junk) . It doesn't fall below the "industry standard" of about 97 percent on coarse test dust (in fact most OCG will show about 98+). It's likely a K&N (which is probably the best of the OCG filters out there) would meet the minimum standard for efficiency required by most vehicle and engine manufacturers, outside of commercial agricultural and heavy duty applications. Remember... minimum standard.
So yes, you can safely say OCG filters are "adequate" in the efficiency department but they are nowhere near the top of the food chain there. In general, they are chosen for their high flow rates and longevity. This is why they are synonymous with performance engines. Performance engines are usually operated in fairly clean environments, because they are fun vehicles rather than daily drivers or workers, or they are used where the rigors of racing will overcome the engine long before the increased wear from less-than-stellar filtration efficiency. And if a vehicle operates in what is largely a clean-air venue, air filter efficiency is less an issue.
IMO, OCG filters are a legacy product from the days when OE air filter efficiency was generally low, flow rates were abysmal (it was the housing design as much as the elements) and when you used the old filters in dusty environments, they plugged up quickly. A K&N was a Godsend in that situation. You got an air filter that let your engine actually BREATHE, it held a lot of dirt, plus the efficiency was about the same as the filter you replaced and often better. What was not to like! You were an idiot not to glom on!
Air filter technology has marched well past those days. The OEM are largely designing filter systems that have adequate if not superior airflow to more than meet the engine's needs (there are exceptions, of course). Average efficiency is 96-97% plus on FINE test dust (99+ on coarse) and capacity has doubled or tripled versus the olden days. In that environment, it's harder for a OCG filter to compete based on the facts but legend and lore are carrying them beyond their era a bit.
With any engine, cleaner air is best from the wear standpoint as the dirt that comes in from the intake is the worst for the engine and it can begin a chain reaction of wear... wear begets wear. And you want a filter that gets out a lot of the fines because the fines are the bits that get between the rings and cylinder the easiest, causes damage there and then gets into the oil and because these fines (1-20 um) are usually too small to be caught by the oil filter in large numbers, so they continue to circulate and cause wear.
In the past decade or so, air filter rating has been standardized to the ISO 5011 protocol but remember one important fact... the test allows the use of EITHER coarse or fine test dust. In evaluating filters, you need to know which. A filter that shows 98 percent on coarse will show 92-94 percent on fine. If you see a rating and it doesn't specify which, assume coarse because those are the best braggin' numbers. And yes, you can find filters that will produce 99+ percent on FINE and those are the best choices for engine longevity. Remember that a finer filter may have a shorter service life, but the modern synthetic media filters can combine high capacity with high efficiency. Short service life is more an issue with high efficiency cellulose media filters but even then, this can be accounted for by an increase in media (more pleats) or a larger filter (if the package size will permit... i.e. more underhood room for a larger filter).
So, I guess the question you have to ask yourself... and I won't call you a punk like DIrty Harry might... what is it you want to achieve? If it's a stock vehicle used as transportation, what's the advantage to likely taking a hit in the efficiency department? If it's a high performance car and you are considering an improvement for performance sake, the OCG choice is nearer the mark but consider that many of the dry aftermarket elements, like the one you mentioned, usually have efficiency superior to OCG but with virtually equal flow rates per square inch of media and if they don't, they just engineer MORE media in the filter to make it so. I could quote chapter and verse on some of the media I've looked at, but since I've done all that before, I'll suggest you just look back at my past posts.
Final thoughts here. I was given a chart by an engineer at Parker filtration that illustrates very well the effects of low vs high efficiency air filtration.
Code:
For Every 10 Pounds of Dust Drawn Into the Air Filter Inlet:
EFFICIENCY OF FILTER DUST INTO ENGINE
99.95% 0.005 lbs.
99% 0.10 lbs.
95% 0.50 lbs.
90% 1.0 lbs.
