Castrol GTX it is then. Do you reckon semi or fully synth is best? I do around 150 miles a week and drive the car fairly hard now and then, but don't constantly drive like an idiot and I do wait for the car to warm up obviously before giving it a blast.
I will also be topping up the oil myself every now and then whilst getting an oil changed every year.
If you warm it up, like everything, you will get best performance. You will notice an appreciable difference in the viscosity of 10/60 against other oils. 10/60 only comes into it's own at higher temperatures.
From my (limited) understanding, if they have the same figures, they have the same lubricating quality. However, semi-synths will "go off" quicker than fully synths. If you're changing every 6k miles, semi is fine, if you're changing less often, you need fully synth. This is only what I've picked up from the oilman's posts and I'm no chemist, so I could be wrong!
Yeah sorry Simon, I don't mean to have a go at your have a go at your have a go at your have a go at your, DAMMIT! I don't mean to have a go at your Havoline, I just went to Asda and bought some Castrol GTX 10w40 High Mileage 4 Liters, cost under £12, bargain!