penzoil makes a 5w-20, but since i get 20% off at honda it's like a 1.80 a qt so that's what i put in my girlfriends 02 civic. i would use mobil 1 5w-30 over royal purple or amsoil 5w-20. if you look at the bottle of honda oil, check out who makes it.

i switched to syn at 90k on my old motor, i had no problems.

i would think anything more than say 125K i wouldn't bother switching. if you decide to switch at higher mileage you should mix it with dyno oil for a 1 or 2 oil changes before going full syn.
.02$