"10W-40 conventional oil? Stick a fork in the rotting corpse"
"10W-30 = gone!"
With the high quality of modern conventional base oils, I don't think any grade of oil is obselete, it just has to be used in the right application. In a thread about 10W-40, a member comapred UOA's of 5W-30, 10W-30 and 10W-40 conventional oil, and found that they all basically sheared the same amount, so no grade is worse for shear than another. We also know that modern detergent packs clean up well after this shearing, so an engine gumming up from oil residue is not a problem anymore. So the argument, don't use (10W-40) oil, it'll gum up your engine is what is obsolete.
Most engines will live a long, happy life on 5W-30 oil, but we have to admit there are certain engines that do better on thicker oil. GM OHV engines seem to be one of them. In the UOA section, there are several UOA's on Cavalier and Sunfire 2.2's that show they produce lower ppm wear numbers with 40-weight oil. Also, being a slow-revving, OHV design, a thicker oil probably won't make them noticibly more sluggish, so it is probably a good grade to run. This coming summer I fully plan on running a 40-weight oil in my 2.2 Cavalier, after seeing the success Cutehumour and others have had running this weight in GM 2.2 OHV's.
On the other hand, a high-revving, DOHC engine, with lots of cams and narrow oil passages high up in the block will probably benefit from a thinner oil that can get up to those parts faster, and not put as much drag on all those spinning parts.
People bash 10W-40 conventional oils these days, but one thing to keep in mind is that it probably saved more engines than we want to know in the 1970's, when it was at its zenith. How many poorly tuned V-8's that washed their cylinders with gas stayed alive b/c the 10W-40, sheared down to only a 30 or 20 weight, instead of a 20 or 10 weight for a 10W-30, and still protected the bearings?
Modern 10W-40 deserves a LOT more respect and consideration than it gets!
