Traditionally, the only purpose of the downstream oxygen sensor is to confirm catalytic converter function. The ECU does not make any changes to engine operating parameters based on the downstream oxygen sensor. I assume that is the case with our systems as well. They system will of course, make adjustments based upon the upstream oxygen sensor.
Metal shavings at 50k is something to be concerned about, since it is far, far, far, far, far, far outside the break in period. Since this is related to the modifications done on the engine, it may be prudent to back off on the power, possibly even undoing the modifications and returning to stock. Besides a complete tear-down and inspection, it may be possible to just pull oil pan, as a first step toward inspecting the crank main bearings.
Regarding the filter, the only way to achieve "high" flow, is to either increase media surface area, or reduce the effectiveness of the filter, or both.
Metal shavings at 50k is something to be concerned about, since it is far, far, far, far, far, far outside the break in period. Since this is related to the modifications done on the engine, it may be prudent to back off on the power, possibly even undoing the modifications and returning to stock. Besides a complete tear-down and inspection, it may be possible to just pull oil pan, as a first step toward inspecting the crank main bearings.
Regarding the filter, the only way to achieve "high" flow, is to either increase media surface area, or reduce the effectiveness of the filter, or both.