everyone seems to have have a different opinion on this, but i prefer Amsoil for the crankcase / engine, and Golden Spectro Heavy Duty Platinum 6-Speed for the trans (75W-140), and im happy to say i no longer have a need for primary fluid due to my open belt drive
Thing most important (other than lubrication) is an oil's flashpoint. Amsoil, Redline, Mobil 1 V Twin all have flashpoints higher than others, much higher than dino oils.
Flashpoint is the temp an oil breaks down at, so the higher the better.
I used Mobil 1 for a while but when I found an outlet to get Amsoil for the same price, I tried that and am very happy with the results.
As an example of your statement my 72' El Camino only had 5 lbs oil pressure at idle with Mobile 1. All I did was change it to
Castrol GTX 10-30 and oil pressure went up to 30 lbs at idle.
Put some STP in it and you could have gotten 60 lbs at idle, but it wouldn't protect your engine any better than the M1 at 5 lbs. You're putting too much emphasis on pressure and not flow. A 10-30, a 5-30, & a 0-30 should have the same viscosity (10) at operating temperature, whether they're Dino or Synthetic.
On a serious note, I use non HD oil when I need to. And only dino. I got tired of the ticking synthetic was causing because it's thinner.
Synthetic oil isn't "thinner". A 50 weight Dino should have the same viscosity as a 50 weight Synthetic when at operating temperature. Your Dino oil may have different additives that affect the ticking you heard. Synthetics claim to fame is that as the temperature of the oil decreases, it's viscosity increases at a much slower rate than Dino oil, resulting in increased flow on startup where most wear occurs.
I have used Mobil 1 in all 3 holes with the Mobil 1 gear lube in the trans for 36,000 miles now. It is a gearbox after all. Every test report I read had Mobil 1 placing second, with the exception of the Mobil 1 test. Thats why I use it.