Actually I think you're right- 5w-30 is what they probably ran.
Honestly, I have no idea how to read the oil pressure gauge. It goes up n' down while driving so as long as it's moving I guess it's fine.
As for how much higher, I'm not sure but it doesn't seem to be reading much higher than...
My unscientific impressions-
I just changed over to Chevron Delo 400 15w-40, Toyota OEM filter.
PO had 5w-40 oil (a guess, it is thin) and ProMotive PH1A oil filter
I noticed:
-engine sounds much quieter at idle. "smoother" sounding
-oil pressure gauge stays up at the 3/4 mark for awhile...