Just a thought -
If 5W-30 and 20W-50 both yield the same
oil pressure in your engine, it could be that more of the thicker
oil is being routed through the bypass.
Cobras have a lot of extra plumbing for the
oil to pass through (cooler and associated lines), heavier oils may not want to make the trip. If so, you will have the usual extra wear from less oil being pumped to the usual places (cams, rockers, rings) as well as the wear to the components driving the oil pump which has to work harder to push the heavier oil.
When I went from 20W-50 to 5W-30 (Mobil1) my oil pressure went up!
Bob