There's nothing wrong with the Syntec 5w-40. I've run it in my VR6 at least a couple times and it's worked well.
The problem is, nobody really knows a lot about the stuff. And it only made that worse when it switched from made in Belgium, to made in US. Base stock is unknown, and I'm unaware if any VOA's were posted after the switch to US made. Still, I'm not sure you can really go wrong with it, it's likely as good or better than Syntec's other offerings, and possibly Mobil1. I'd try it in your engine and see if it likes it.