Yes those two oils are the next step above the Mobil 1. The Mobil 1 is a good quality synthetic, the Silkolene and Millers are ester based synthetics, meaning they are better lubricants, more durable and more stable in harsh conditions. They are also slightly thinner than a 15w-50 when cold so they give better cold start protection.

I didn't notice Pacwest is from Canada, but that may explain the reasoning if they have a similar attitude to oil as in the US, ie use basic cheap oils and replace on a very regular basis. It's odd in a way as some very good oils (Redline and Amsoil for starters) from the US, but they use very outdated oils instead.