I did a brief experiment a couple of months ago with IR temp gun, only measuring surface temps as I dont have an inline set up on the rail like you do. Not exact but it does help indicate cool and warm spots.get a temp gun and do some work. It's not too hard. Everyone needs their own baseline. To gauge with.
Ambient was 80F and after thirty minutes of city & hwy driving I measured the following:
FPR: 138F-outlet/inlet
Return Line: 128F
Fuel Filter: 120F
Pulse Damper: 139F
The variance is 40~60 degrees surface temp to ambient.