I use Castrol oils and always have since my first car, a Mazda R100 for the few that might recognize it's importance to performance cars.
Why? It's a good oil and a offers a free warranty on your engine. I have never had to use the warranty but I was relieved to know it was there. Almost 300K on my hard driven BMW 320 IS and no oil burning....The FiST will like my other cars be around for many, many miles so I will again use Castrol. After break-in I will switch to the Castrol EDGE Platinum with Titanium and be relieved that the engine/turbo will be covered for 15 years and 500,000 miles if anything does happen. The FiST engine is producing over 2 HP per cubic inch and under those harsh conditions I think a long term warranty may be needed, I just don't see this little powerhouse lasting hundreds of thousands of mile of my spirited driving, could be wrong and hope I am. And Mods are OK with the Castrol warranty as long as you do not engage in "competition"......
Is Castrol the "best" oil......who knows. But I'm going to change my oil regularly with a premium product anyway so why not use a free warranty? I like free and hope I don't use it. And no, I have no financial interest in Castrol nor BP. Actually after what BP did to my home state of LA I should hate BP! But Castrol has served me well for over 40 Years....long before BP bought them out. On the other hand one of my sons rebuilds/resells GM LS series V8 engines and does not like Castrol at all and thinks all dino oil is trash. And I have seen the dino oil sludge in rebuilding one with him, I was surprised for the low miles on the engine at the gunk in the oil pan. I wonder now what the inside of my BMW's oil pan looks like?
That is my two cents worth but the bottom line is this......change your oil often and don't use cheap oil! I have never heard of an engine damaged by changing the oil too often.