Just today i put 0W-40 (Mobil One) In my car and it runs fine, maybe even better when cold than my old Mobil One did (5or10W?-40) (whatever the one you buy in the shops is)...
i have noticed that when cold the oil pressure is much lower than my older oil. when cold the old oil sat just above the 4 now mine sits just above the 2. the oil pressure only changes slightly from cold to hot.
the engine is running fine, isn't burning oil or anything
i have a 1997 tho, so it may have les engine wear than other R33's...
Anyway thats my 2c.