There are times when I think the words like "better" or "best" should be blocked from this site. They are so subjective, because they are used without clear definition.
Q: "are synths actually better than conventionals?"
A: "depends ..."
Better at what?
Temp extremes? Probably. I'll give two examples. Extreme cold. I apologize; I meant E X TR E M E COLD. Like WELL below freezing cold. In this case, a group III, IV, or V will pump a bit easier, getting up to pressure a bit sooner. However, zero degress-F and a conventional 5-30 can still get along quite well. Or, look at extreme heat. By extreme, I mean WELL past the designed operating temps for the application. Example: I have had the misfortune of having two of my vehciles overheated from failed cooling systems. My wife's van (water pump) and my father's Taurus (freeze plug). Both went into the red zone and were driven way farther than they should have been before shut down. My Taurus coked up the rings (see oil additive thread by me) because it was on conventional oil. The van, however, didn't coke up; it was running on synthetic (PP at the time, IIRC). Subsequent compression tests conducted showed that the synthetic tolerated the extreme temp better. BUT - IF YOUR ENGINE NEVER SEES THESE EXTREMES, THEN "SYNTHS" ARE NOT NEEDED! I don't believe it's fair to blame a conventional oil for failure when unrelated mechanical failure was the root cause. Had the Taurus been pulled over immediately, there likely would have not been any ring coking. So the answer here is a Syn might be "better", but only if you allow some undesirable condition to occur. If not, then a conventional oil will do just fine.
Better at what?
Wear Protection? Probably not. There are many, many used oil analysis that show good wear results with "conventional" oils. The thing about wear protection is that it is always a matter of changing ANY oil before contamination, oxidation, insolubles and such degrade the oil to a point of ill-advised continued use. I want to be careful in my description of wear protection here. I mean to say that an engine/oil combination that is studied in long term statistical analysis using consistent used oil analysis and looking at ranges and trends. Anyone can show a one-time post where brand X performed better than brand Y or brand Z, but these are meaningless unless the variables are controlled. Too many people use a single UOA as justification to use or reject an oil. Too many people here hop-scotch from one brand to another, with the misunderstanding of how used oil analysis should be used.
Better at what?
Lasting longer? Probably so. Here is where "synthetics" really shine. They can take the environment for a longer period of exposure. If you run long OCI's, use premium filtration, and used oil analysis, and drive many miles a year, then SYN's are probably a good fiscal decision. But if you can't mentally get over the hump of the 3 month/3k mile OCI, and/or you only drive 10k miles a year or less, then Syn's benefits are not realized. Period.
So is it right to choose a synthetic over a conventional? It depends on the appliation. My 1966 Mustang which is used for summertime Sunday cruising, for a total of 500 miles a year, DOES NOT qualify for synthetic in my fleet. Nor does my rototiller, or other low-use, limited extreme equipment.
However, my wife's van (previously noted risk!), my truck (winter 4x4 and summer towing of travel-trailer) do see greater risk and/or length of OCI service, so I choose the advantage of synthetics.
There is no right or wrong answer; there is an appropriate answer for each vehicle, in a specified environment, with a recognized risk level.
