ive not seen the Castrol RS 10W-60 variety on sale for months, and the website has been down the same length of time
Mobil 1 15W-50 (M/Sport) is a very very good oil, however its crap for cold starts
trust me mate, if you want the best, get Silkolene Pro R 15W-50 if thats the kind of ratin your lookin at, you will never ever use any other oil in your car once you try it, its very very good, and has a very high ester content which means it will stick your engine like magnatec does......only better
its red too
if your anywhere near the north west i could get some for you if you want....its £34 for 5L compared to the others £34 fr 4L