Castrol synthetic or Valvoline?

Ottmundr said
Hey Trailbeast,

Did you see the thread where there was a link to a very interesting oil test results site? It's called 540 RAT tech facts. A lot of reading but very worth it.

Ok, maybe not quite the answer you are looking for but I hope it helps;
After reading it, I decided to try out the 5w30 Quaker State Ultimate Durability in the gold bottle. As soon as it stops raining here for long enough for the pavement to dry out, I'm gonna change my oil and try it for a few months, then I am going to give the 5W20 Valvoline MaxLife High Mileage, API SN, dexos 1 approved, synthetic blend (red bottle) a try for a few months. I don't really care about brands so much as I care about hard data.

Thanks as I had not seen it, but will.
The only problem I have with the high mileage designations is that they swell rubber seals as part of their function, and I don't need or want that.

Dartish said
How cold does it get where you live? I've been running Kendall 10 w40 synthetic blend all winter in my 360 just because I get it for $2.69 a quart. I used to run 10w30 Valvoline in my old daily driver dart when I had it. Alway liked it cuz it seemed to stay clean longer

In the winter it can get down into the low teens, and summer over 100.
I wouldn't mind switching it up for season changes as that is about the normal intervals I change the oil anyway, but I was thinking one weight oil might handle both. (that's why I asked about the different low numbers in viscosity)
Valvoline and Castrol are the only two standard type oils I have ever used in my own stuff, but now I want to go to a full synthetic with the new magnum.
I can get the Castrol full synthetic for about 17 plus tax for the 5 quart jug.
I used plain old Castrol GTX 10-40 in my old motor because it was an original 70's 318 and used a half a quart or so every couple of weeks and was cheaper.
Now that I have this new motor that doesn't use any at all I figured it best to use the synthetic, since the motor was basically designed for newer oils wit the thinner rings and all.