oil
I really don't think it would be worth trying to mix good synthetic with decent "dino", you would just end up with a mediocre semi-synthetic. You could just buy it and save the trouble. I don't think that most semi-synthetics are worth the money.
I've been running M1 0W30 or 0W40 with 7500 mile oil change intervals since the car was new. I just changed out the cam and there were no oil deposits what-so-ever. Looked like a new engine, timing chain was like new. There are plenty of sites to look through on oil. Here is a good one-
http://theoildrop.server101.com/cgi/ultimatebb.cgi
There are a few great oils out there, there are alot more mediocre ioils that cost pretty much the same as the good ones. Look through some of the oil analysis and and you will get a idea of the great oils.
In this case i would recommend using their 10w30 over the 5w30 though, because it's thicker at 100C. Plus the fact that a 5w30 that isn't a full synthetic will usually thin out quite rapidly.
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The 0w30 Castrol I use is actually thicker at operating temp than Mobil 1 10w30, in fact this oil starts out almost as a 0w40, and after 6200 miles when I did an oil analysis on it, it had in fact slightly thickened into a 0w40. The wear numbers were incredible, especially lead, which is the indicator of bearing wear.
That's only my opinion,,,, do some searching on that website I posted and make your own opinion.
(as clean as a whistle) no deposits or sludge anywhere. I'm sticking with Mobil1 for the life of the engine. 

