I have formulated both fully synthetic automotive engine oils and conventional oils. The modern hydroprocessed base oils rival synthetics in terms of stability and response to antioxidants. They exceed synthetics in some areas such as additive solubility and can even exceed synthetics in terms of volatility (oil consumption) in the lower viscosity grades.
The area where synthetics excel is in extreme low temperature flow and pumpability. By this I mean below -30°C (-22°F). All SAE 5W grade oils (like SAE 5W-20) actually meet engine pumpability and flow requirements at -35°C and are fit for purpose at that temperature. But synthetics do flow a little faster at those extremely low temperatures.
Other than that, it is far more important to change your oil than worry about using a synthetic oil. The engine tests used to certify all engine oils today are so severe that only the best quality severely hydroprocessed base oils will meet the requirements set by ASTM, SAE, and OEM's.
Just to make this discussion interesting, Shell has a fully synthetic oil made from natural gas. Their Gas to Liquids plant in Qatar produces the base oil by hydrocracking synthetic wax into isoparaffinic base oil. This is the ultimate synthetic base oil that has properties much like base oils derived from polymerization of olefins but also has properties of conventional base oils. Essentially the best of both worlds. I have made these base oils for another company but we were not able to commercialize the process due to financing issues.
Engine oils are exceptionally complex products that are highly regulated and tested for conformance to OEM requirements. Trust any name brand product that meets your car's requirements and change it at regular intervals with a good filter. I got 220,000 miles on a Grand Cherokee 5.2L that still didn't burn more than a few ounces of oil between changes. I used Chevron Delo 400 SAE 15W-40 for the life of that engine and it was sparkling clean inside. It died when my daughter rolled it on a dirt road, otherwise it would still be running.

 

I use Penzoil Ultra Platinum (PUP) 0W-40 in the Charger with the SRT filter. The Jeep gets PUP 5W-20 with the MOPAR filter. The BMW gets the dealers 0W-20 and the OEM filter. OCIs for all are every 6 months or 5,000 miles whichever comes first.

 

Full synthetic is never overkill in any vehicle. To the guys with the smaller engines...it’s even more important if you tend to drive “spirited” occasionally. Those 4 cylinder rigs tend to rev pretty high and would possible benefit more with full synthetic then some of the v8’s. My car only has about 40k and it gets full synthetic every 4-5k. I have a 06 Tahoe that’s my daily and it gets full synthetic 5-6k. The Tahoe has just under 300,000 miles and runs purrfect. Not even a lifter tic that almost everybody else deals with in the 5.3. I have a 1999 ram 1500 that has seen full synthetic since I bought it with 15k. It has 225,000 miles. Been through two transmissions, 3 plenum gaskets, but engine is clean and runs great.

It’s worth every single penny to put quality oil and filters in your vehicles.