If it's the same viscosity and the same temp the pressure should be very close. But that's not what this post is about. The only reason I would question the filter is that the owner stated it happened right after an oil change. If the pan is filled to the correct level, the only other item that changed was the filter. Is it possible something else failed? Sure but I would start with what was changed first. A filter swap Takes 5 minutes and less than $10. The pressure number is overrated. However when there is a drastic change in that number we have a problem. Example car "A" has 40 psi at 6000rpm since it's been built, no issue. Car "B" had 90 psi at 6000 rpm when it was built,but all of the sudden it has 65psi, This is a problem. The fact that thicker conventional oil creates a higher reading only because it has more resistance to flow. Oil does two things, #1 provides a hydrodynamic wedge that keeps metal parts from touching. #2 provides cooling. More flow equals greater cooling. Thinner oil flows faster. It's a win win for the motor. I run 5/30 synthetic in all my bracket race motors. Stock eliminator motors get oil that's even thinner. Thick glue is old school. Look at new Hemi, LS, and Coyote motors. All have synthetic thin oil requirements. In summation there is NO WAY synthetic oil would cause the issue listed in this post. I would suggest anyone wanting to expand their knowledge of oil protection to read here.
I break in on conventional mainly do to cost. Your going to dump it after 30 minutes. New car manufacturers break in with synthetic, but no break break-in with roller cams. I run my 900hp bracket for 100 passes between changes with synthetic. The bearings are then inspected. 200 passes same bearings.
