Hi
I agree to an extent - a 5w-40 synthetic from a reputable company should be absolutely fine for a road car. There are a few really basic 5w-40s around that aren't exactly what they say they are - one oil company tested a few and found that while they said 5w-40 on the can, when tested, a few of them were shown to be well out of grade. One was a 20w-40, others were 5w-30 and 10w-40. That's part of why an oil from a reputable company is worthwhile, cheaper ones have less quality control, leading to more errors like that. I'm not saying everyone should buy Nanodrive, Pro S, Castrol Edge etc, but even a cheaper oil from a reputable company is better than a budget oil.
Another thing that happens with cheaper oils is that they will say that the oil 'meets the requirements of' or 'suitable where (a specification) is required' etc etc, but unless an oil is approved to a certain specification, those comments are basically worthless. They can be as misleading as the incorrect grades on the can.
Basic oils don't last as long as quality ones, so need replacing more often and can end up costing more in the end (and that's just in oil costs, not taking into account extra wear). One customer saw an extremely cheap 5w-40 from a motor factor and put it in his track car. After 2-3 laps the pressure dropped right off and after giving it a chance to cool down, he took it out on track again and the pressure never came back up properly. Okay, that oil was never designed for track use, but that just accelerated what happens on the road.
Back to topic - The Nanodrive oils are really popular, even though they cost a fair bit. Generally people buy it and stick with it at the next service, rather than going for something else, so to me that says that they have found the difference in price is worthwhile. A lot of it might be in their mind, it's difficult to quantify how much difference it makes without a lot of track use or a rolling road, but when it has been done, the results have been impressive (have a look online for the Fast Ford/Vauxhall test and there has also been a recent test in Banzai). Whether or not the extra BHP matters to you, as a road oil there is another benefit - increased mpg. One guy with a Integra went from a normal 5w-40 (a decent one, not a cheapy, but not a performance one either) and was getting 32.5mpg, then changed to the Nanodrive 5w-40 and the mpg went up to 35.5, if I remember correctly. Okay, it was based on his data rather than proper department of transport testing, but it seems to be quite a bonus in economy just from changing the oil. When I mentioned it to Millers, they said that was pretty normal based on other feedback they had received.
Cheers
Tim