I couldn't argue with that.
That NO oil company is a philanthropic oganization is a given.
As regards Castrol's sites, the Uk one is a bloody mess, ALL the engine oils are referred to as GTX something or other, and a good number of the ones listed are obsolete (no longer made) and have been for a long time.
Oil specs, standards (and availability) are as you say variable by market, and not always logically so - Castrol TAF-X (fully synthetic transmission oil) isn't officially available in the UK; yet it's the standard transmission oil for cars such as the Lotus Esprit, a whole host of Renaults using the same transaxle, and many more besides!
As regards using w-30 oils in high ambient temps. You may remember MB went through a phase of doing so, and it cost them a fortune in warranty claims. And really, if you have more than 50,000 plus on the clock sans rebuild, fully synthetic of any kidney is a no no for any engine - which you more or less acknowledged previously. The idea of using even lower w-20 grades in high ambient temps is certain engine suicide and no mistake. A monograde SAE 30 would hack it up to 40C/104f, (SAE 40 higher still) but couldn't handle the low end running out of puff at 0c/32f.
As regards 'getting what you pay for' or what you think you're paying for, only having samples independently analysed would prove anything - and who's likely to instigate that? Not an oil company for sure!
Cheers,
T
Addendum: 5w-30 Edge is NOT recommended for useage as you said. I would suggest reading the correct product data sheet, not the general overview. Also, I wouldn't put any store in any recommendations from Castrol or ANY oil site. Very many of them are ludicrous beyond the point of abject stupidity - including the idea of using a w-20 oil in 'all conditions'! If you don't believe that, try running that Mustang thru the Arizona desert in summer - and do remember the auto club number and your mobile for when the engine seizes!
Having perused the Castrol site, where a 5w-30 is 'recommended' for the 4.0 6 cyl Mustang, one must assume it is there by mistake, as recommendation for the 4.6 6 cyl is a 5w-20.
Patently some anomaly there, and clearly both wrong as no oil of either viscocity can adequately protect an engine in high ambient air temps; not because I say so, but because no matter how much technology you throw at the problem, you cannot make a w-20 or w-30 which will protect an engine at high ambient air temps ). Interestingly, the same site recommends for the V8 Mustang a 5w-50 which actually makes sense!
The problem with the Castrol website appears to be with the temperature option not being avilable for all vehicles. Were you to put in the details for a Triumph TR7 for instance, you will find if you check the -4 to 61 (farenheit) option, it comes up with a logical recommendation of a 10w-30 oil. Similarly, if you check over 32 (centrigade) it again, logically, comes up with 20w-50. They do, of course make a point of plugging 'Edge' as the first option in some cases, but then they would - it costs most, even if it's not really ideal for the said application!