I personally think RP has been more hype that factual. When I first became an Amsoil Dealer and heard about RP, I asked some of the older Dealers if they ever heard of it. They said it was a small synthetic company and many petroleum oils performed better. RP has done a lot of marketing in the performance community, so now their name is widely known in that group. They do have two different lines. The usual line you commonly see is a blend, unless they have changed it (it has been a few years since I looked into them and how they compared). Their Racing line was much more expensive and was a full PAO synthetic. Last year there was an article about synthetics in MM&FF and the RP rep was quoted as saying all synthetics start out from crude. This is false, and leads me to believe that RP is now a Group III hydrocracked petroleum oil that the API considers a synthetic and what most of the mainline synthetics have switched to.
There are three different "synthetics" out there, but really no one advertises which one they are. This is based on the Groups of oils the API has designated. Groups I and II are petroleum, II being the common petroleum we use most today. Group III is a petroleum but even more refined (hydrocracked) and falls within certain specs that the API said can be called a synthetic. Castrol Syntec was the first to use this and Mobil lost a lawsuit over it. Since then, nearly all synthetics have gone to a Group III oil falling within the certain specs required at one level or another. Group IV consists of all PAO oils, which currently include most of the Amsoil lines, Mobil 1, and RP's racing oil, if the rep was wrong in that article about their oil being from crude (or that's how I understood it). Group V is considered "everything else" but usually consists of Ester based oils. Redline falls into this group and is an excellent race oil because of it. Both Amsoil and Mobil were Ester based back in the 70s when they came out, but Esters have the tendency to want to retain moisture and the reason both companies switched to a PAO base. Redline needs additional additives to address this issue. Mobil uses additives to enhance their oil and Amsoil actually uses Esters as additives to get the best of both worlds, a more costly approach, but one they believe in to meet the extended intervals they promote. The Amsoil XL line of oil is actually a Group III but uses a higher grade of base stock than what many others use and one reason why this lower tier oil performs well when compared. The 5W-20 they have is in the XL line and has done well in testing. One of the Direct Jobbers I work with did some oil analysis in his Ford and after, I believe, 8000 miles the oil was still usable and he did gain a few extra MPG when comparing it to our 5W-30.
Check the specs between the oils, this will give you some idea of the differences. I'm hoping Amsoil will show some RP comparisons in the future. I've gotten some info in the past, and done my own spec comparisons, but hope it will one day show on some of the automotive literature they have. Amsoil recently started showing them in their Motorcycle Oil testing and comparison lists and RP didn't perform as well as many of the oils tested. They had tested 20-25 different oils and I believe there was around three times the wear when comparing their Motorcycle Oil to the Amsoil Motorcycle Oil.
As for price, you're right about it just costing a little more, but as you said, with most of us, it shouldn't matter that much. Also consider how much the prices for oil has gone up over the past year or two. I'm seeing petroleum oils hitting the $3 per quart range and higher. Synthetic is around twice the cost, but with some of these oils you can easily go twice the distance (check if it is warranted for this though) making the actual cost the same, or less.
My personal choice, if I wasn't using Amsoil, I would probably use Mobil 1.
