I run 20-50 Castrol

 

10-30 Royal Purple

 

5-30 RP here

 

different oil weights haven't affected my oil pressure...
ran Castrol GTX 15w40 first few oil changes, now running Pennzoil Platinum 5w30 and see no difference in oil pressure...even between conventional and synthetic...
installed a new GM oil pump when building motor and it
runs in excess of 60 #'s , regardless of oil weight...
main difference I've seen w/ the built motor is the oil consumption...
usually have to add a qt or two between oil changes...mostly following track days...

 

20-50RP with my Radix

 

10/30 Rotella, and yes the do make it. No cats here though, that would probe kill them.