Well,
Ive always dissliked Castrol RS in the YB and CVH Turbo as many old school forum members will remember as ive had a few heated discussions about it causing follower rattle on Hydraulic Fords (Whatever happened to Andy? That argument was legendary.. top man ) I dislike both its cold thickness and its hot viscosity when not used with an oil cooler. Ive always been convinced it is NOT what it says on the tin.. Its deffo not made by Ronseal

I do however love Mobil 1 motorsport and have used that in customers cars for many years unless specifically asked to fill with RS (Some people request only that, so i do as im asked)

After a chat with Simon at Opie i took delivery of some Silkolene Pro S 10w 50 and tried it in my own YB for a while.. results?

This Pro S appears to be better when cold and better when VERY hot for the YB. In fact, i concur that engines ive drained of RS10w60 and refilled with this oil appear to have gained a few noticeable Gee Gee's. I put this down to the frictional losses dropping within the engine now its having an easier time pumping the oil around. I dont believe it protects any better or worse that M1 MS but im convinced its far better than the RS10w60.

With regards the pumping pressures of 10w60, i have noted over the years that most of the oil pump driveshaft failures ive seen and heard of that have wrecked engines were running this hard to pump 10w60 RS as well..

Final 2 comments:
1) Its red. Sound a daft point? Its a great point when your oils always clean and you cant see it in low light on teh dipstick

2) It comes in 5 litres. Bargain IMO.

Hope this is the kind of feedback you wanted and im not just waffling.