Napa is Valvoline where the additives are concerned, so if you would normally run the Valvoline conventional say 5K, then this oil will do exactly the same job in the same way pretty much.
As far as the synthetic goes, again, pretty much synpower, same additives, even same amounts of it. The only thing I suspect is different is probably the amount of PAO used and I only say that due to the difference in viscosity at -30 with synpower being a little lighter. Valvoline advertises something like 5-10% PAO used in its makeup, and I would think the NAPA probably has 5 or less %. Check it out for yourself at pqiamerica.com. If you would run synpower to 7500 or so, then the napa synthetic will do the same job with no worries, little to no difference. I just bought a case of it myself, half the cost of its twin so why not? Pretty good UOA's on here too, seems to hold TBN retention well and very low wear numbers on average.