I have used the Walmart Supertech Synthetic on and off over the years. I see that Citgo now makes it for my area. Any thoughts of how well Citgo is compared to other brands? I usually do 4000 mile oil changes, so it seems like a good buy for my use. I'm sure it isn't in the Mobil 1 or Pennz synthetic leagues, but for 4000 mile oil changes, I figure it will keep things clean and well running. Any thoughts?