Caveat:
The recommendation of grades of oil and types of oil is easy.When recommending brands however, one will often shortchange some good oils, one may have no experience with ( example MOTUL?)
95 J30 with 90,000 miles:
Since you live in Atlanta and drive mostly on the hiway a 40 weight oil is what you need.AMSOIL makes an excellent 10w-40, which would be a first choice if availabilty was not an issue.
Other 40 weight full synthetic oils are.MOBIL1 0w-40 (hard to get, also only at MB and Porsche dealers until recently), besides I think the spread is too wide, from a 0 to a 40, even for a full synthetic, maybe as a winter oil with not extended drain intervals.
5w-40 Valvoline Synpower, my current favorite it has the 40 weight I recommend and also has more detergents than MOBIL1 which is a consideration at 90,000 miles.(My recommendation)
97 QX4, 85,000 miles short trips:
Because of the short trips I would like a formulation with high detergent (such as Valvoline SynPower, valvoline Durablend, AMSOIL?, MOBIL driveclean), BUT because of the demanding driving environment you want a synthetic, preferably a 40 weight again.
Again 5w-40 valvoline Synpower or MOBIL1 0w-40 ( but probably a bit low on detergent).
AMSOIL if you wanna go that route in 10w40 is also great choice.
So again considering availability my recommendation is Valvoline Synpower in 5w-40 (all year round in Atlanta) assuming you keep reasonable oil change habits.
(kinda Ironic that 2 differnt requirements worked out to be the same oil).
If you have a habit of extending yours, say past 4000 miles, then you should go with a more stable 10w-30 formulation.
The 5w-40 SynPower has probably too large a spread for extended drain and I would not leave it in for more than say 4000 miles tops.A 10w-30 can stay in longer than a 5w-40.Also if you like to extend your drain intervals definetly avoid Castrol Syntec (Class III base stock).
SUMMARY:
ValvolineSynPower in 5w-40 is my recommendation for both vehicles , works out well too so you don't have to keep two oils on hand.
But if you like to extend drain intervals much beyond 3000 miles and you are confident you engine internals are clean, MOBIL1 10w-30 is not a bad choice either.Or Exxon SuperFlowGOld synthetic in 10w-30, has almost the exact same performance specs as MOBIL1 for 2/3rds the price of MOBIL1.
Fred...
you don't wanna go to the 15w-50?
And for them to stay in business despite the big guys' competition, they must have a good product.But a aynthetic it isn't.Which is why it wasn't included in my poll.