I can kinda see where some would see Mobil's marketing as a gimmick. Most SM rated dinos can easily do 5000 miles, and even up to 7500. Mobil is getting unknowing customers excited that their oil can go 5000 or 7500 miles, while neglecting to tell them that is nothing really special nowadays (I know it's not their responsibility to tell them, but they're still blatantly playing on the average customers lack of knowledge). To me, that is a little sleazy and under-handed.
I also do not like Exxon-Mobil's latest earnings. The company profited $10.3 some billion last quarter. That's a profit of about $3.5 billion a month. And I'm paying $3 for a gallon of gas? BP earned $7 billion in the same time period. So no oil company is on my favorite company list. I understand they're businesses designed to make money, but there needs to be a little compassion. I am normally extremely conservative and believe in a small government, but I would support the government capping profits on gasoline. Gas has become a necessity in today's society, just like water. While I'm getting poorer spending $3/gallon for gas on a disabled vets limited income, the oil company execs are getting exceptionally rich off the poor who must buy their product to even make it to work (public transportation is not available where I live). Not only that, but the cost of everything must rise in order for other companies to pay their transportation costs.
Since Mobil has the highest net profits, I'm boycotting their products. Maybe if I stop buying their gas and oil, I'll hit them where it hurts. So I'd have to choose Castrol for the original question.
Besides, I've used Castrol GTX for years with very good results. I used Mobil 1 5w30 for 2 OCI and had poor used oil analysis. And it makes my Maxima louder compared to GTX and especially GC, but this was the tinner Mobil 1 5w30 of several years ago.
Anyways, those are my scientific reasons for choosing GTX. But in reality, either would probably do very well for 5000 mile OCI's.
Dave