Hi all just thought i might add my 2 cents
I have used nearly every oil under the sun Mobil, Penrite, Shell,AGIP,Motul,Caltex.... the list goes on.
I think that the best way too check if an oil works for you is check the state of the oil when you change it...Colour, rub it between ur finger etc...
I have noticed that the racing oils like AGIP and Motul that i have used are only good for sorter periods then 5000KM, like a track day/weekend and then change it. But they do work really well for that time!!!
Till now i have noticed that Mobile 1 is the only oil that has kept its original characteristics...well closer than any of the others over the 5000KM.
So i use Mobil1 most off the time and then put in some Motul if im doing some track/skidpan time.