whats the difference between £37 fully synthetic and £50 fully synthetic?
Higher ambient temps? what do you class as higher?
I use Halfords fully synth (rebranded Comma Syner-G 5-40) changed at regular and scheduled intervals does the job fine. It meets all the industry standards (ACEA A3 B3 B4 API SL SM CF and MB 229.3, VW 502 00/ VW 505 00, BMW Longlife 98) and meets and exceeds Renault's requirements.
You can buy more expensive brands with high specifications, but for me I don't see the point. It's not like it will give you more bhp nor have I heard of engine failure caused by the oil that meets the manufacturer's requirements for that specific engine plus I'm not likely to own the car long enough to notice the benefits, if any, of the protection stated on the label by using expensive oil. Even if you do a lot of track days, just change your oil more frequently, fresh cheap oil is better expensive old oil.
Guy , what is it that Motul may be the wrong choice for everyday driving ?
My car has cams and i take it up to high revs every time ; fast road i would call it not really racing (although? )
I have been putting in the 300V 15W40 these last couple of years. Should i change to a different one ?
It is never tracked (yet). However with no other street traffic i thrash the %^& off of her
As long as you change the oil often enough, the cheaper stuff is fine, but it can be a false economy if you end up buying an oil for £25 and changing it twice. I just had a look at the Halfords site and the 5w-40 Fully Synthetic (hydrocracked mineral) is £34.99. We have the Motul 8100 X-Cess and that is just as good, £28.38 to you and that's before any offers. Silkolene Pro S is £46.58 and Gulf Competition is £44.99 for members of Cliosport and they are top quality ester based synthetics, good for 10k. If you change the Halfords one at 6 or 7k, the better quality oils work out cheaper.
If you have a high bhp car, a better oil can cause a small gain in power just by reducing the internal friction. Admittedly it's small, but I have heard of 15bhp gains in a 700bhp car just by changing the oil. If you need an extra 15bhp when you already have 700 is debatable though.