I am a magnet proponent, but to answer the question you asked ...
No, there are no studies in a bike engine that say filtering all the minute particles out of the oil make a bike engine last any longer than a bike engine is expected to last. Such studies would be rebuild to rebuild type studies and nobody does that on bikes.
But really now, how long is a bike expected to last? 10-20,000 miles? Bikes really generally don't last very long before their owners kill them by neglect. Savage owners expect their engines to last a lot longer than other small bike owners do and we tend to do some things to make that come to pass.
There ARE studies on the big diesel engines in big trucks, locomotives & ships and such that show that fine particulate removal is
very helpful keeping engine oil clean and useable much longer than normal -- and they do track ferrous contaminations, aluminum skirt contaminations, bearing metal contaminations, etc. etc. as their goal on these engines is to go
as far as possible between major rebuilds.
If the oil lasts longer, the engine lasts longer -- that is the expectation these guys run under as they can test and examine the oil fairly easily and frequently to predict the wear levels inside the engine.
BUT, reality says the only plain bearing that we have in the Savage that would demonstratively benefit from better filtration is the aluminum cam bearings in the head. We kill the cam bearings by oil starvation and low idle speeds, so those bearings never live long enough to get eat up with them little ferrous bits.
We do have piston skirts though, just like the big diesel engines do. And we do wear them out and get a case of the slaps at 30-40,000 miles. Could better filtration help here? Mebbe.
You can save some money on filter changes with a supermagnet on your oil filter as you can run the filter for 2 years. Big deal -- that's really small potatoes compared to the cost of keeping the bike running with tires and insurance and gas and all.
So, why do it?
Just because we want to -- same reason as all the rest of the mods we do.