From recent experience, Motul 5-40 x-cess is fantastic. I spoke with Motul about this oil in my 308 which is running very radical cams and stiff valve springs with a crank from a 360 (engine is 3.4L with about 335bhp) and operates in the 8-9k range regularly and Motul advised they are confident in their product as it's used in several rally engines and Porsche cup motors at the 'ring. Mobil 1 would NOT recommend their 0-40w synthetic product to me with my tuned engine but rather recommended their racing formula which will destroy a 355s cats! Motul or Redline 5w-40 get my vote though. Motul rbf600 brake fluid is amazing stuff too.
If you are just going to do normal street driving or some serious backroad driving, just stick with the factroy weight grade:: pick any fully synthetic oil in that range. For these purposes the 0W-40, 5W-40, and 10W-40 are equally good. Pick from one of the top 5-8 motor oils and you are just fine. As you get more serious, you want to look for the HTHS number of the oil. For hot track work you want nothing less than 4.2cP. Slicks might raise the min to 4.5cP.
Ever since my motorcycle racing days, I've been a big Redline fan. I run Redline 10W - 40 in my 1995 F355.
Looky here... http://www.clubscuderia.co.uk/forum/showthread.php?48086-Talking-about-oil-Shell-Helix-Ultra-5W-40&highlight=eurocarparts
