The quality of modern base oil technology has improve so much, that the differences in conventional and synthetics is rapidly shrinking. I would just settle on a quality blend like Delvac Elite, Rotella T5, etc. Base oil categories are determined by the Viscosity Index the oil falls in to. Up to 120 is conventional group II base oil, 120 on up is considered getting into synthetic territory. Mobil Delvac Elite 15w40 has a VI of 140, the 10w30 has a VI of 146. Rotella T5 is around 135. The Schaeffer Oil blend I use is around 155 for both the 15w40 and 10w30 varieties. I use the latter. What is Amsoil's VI? 167 for their 5w40 full synthetic. How about Mobil 1 full synthetic? 156. Only 1 pt better than the Schaeffer blend I use that is considerably lower cost to use. Folks make way too much issue over base oil, whether it is a conventional or synthetic. The blends provide the best of both worlds, provide the best value overall. And in all of this, the additive package that makes up any motor oil determines as much or more how well the oil will perform than the base oil itself. Worry more about the oil makeup (base oil plus add pack) and not spend so much time on just whether an oil is a conventional or synthetic. If it is a blend, all you really need to concern yourself with is the additive package than makes up the oil. i.e. the level of zinc, moly, calcium, phosphorus, antimony, TBN, and all the other aspects of the oil add pack. Yes, you can find this kind of info at places like http://www.pqiamerica.com
The best base oil with a lousy additive package is worse for a motor than a mediocre base oil with a very strong additive package. The add pack is what makes an oil average, good, or great.