Lessee- in the cars I maintain, right now:
1994 Mercury Grand Marquis, 4.6 L V-8, ~108 K: current fill conventional 10w30 Havoline SM w/Lube Control. My mother's car, change oil in it now every 6 months. The 6 months is about up, just under 3000 miles on this oil fill, in the next week or two will change oil & end the world as we know it- by refilling with Havoline 5w20 SM w/LC!
A little experimentation is good for the soul.
1997 Dodge Neon 2.0 L DOHC, ~198 K: just finished up a double-dose of Auto-RX, now on my first non-clean, non-rinse OCI- sort of "rinsing the rinse".
I plan to keep this OCI short, maybe 3000-3500 miles, then a bit longer, then settle into ~5000 mile interval, maybe 6K if UOA says OK. Current fill- ~3.5 qts Formula Shell 5w30 SL/GF-3, + 1 qt Schaeffer Supreme 7000 5w30 SL/GF-3, + ~9 oz Lube Control. At next fill, undecided now whether to continue with Formula Shell, or maybe fill w/Havoline 5w30 SM.
I chose Formula Shell & Havoline because of good UOAs posted on BITOG & low pri$e.
Both cars are running conventional dino oil- sole exception being the 1 qt of BobZoil(Schaeffer blend) that probably has about 20-25% PAO content. I see no need for full synthetic oil in either car- it may be better, but a good dino w/LC is good enough. I do have 9-10 qts of TropArtic 5w30 SM Syn blend on the shelf- bought it out of curiousity & because of its good UOAs posted here.
If I really wanted to go for *long* OCI's again- I'd probably go back to Bobzoil, or maybe try Pennzoil Platinum.
I have about 100 qts of oil stashed now, mostly Formula Shell(all at $1.29-$1.33/qt) & Havoline($1.49/qt or less), & will continue to use until it's gone- includes giving my brother an oil change or two for his Durango 4.7. And I'll continue using Lube Control with any oil, in both cars. The only exception: when doing an Auto-RX clean or rinse.