I have use Castrol Semi Syn for about 2 years, and now i have switch to Q8 and try.
Castrol Pros:-
-take less time to warm up the car in the morning,
-the engine is smooths during driving long distance,
-less tappet sound from engine.
Castrol Cos:-
-the oil is a bit heavy compare to Q8,
-when speed up, the engine feel not as smooths as Q8 oils.
Q8 Pros :-
-the engine feel smooths when start the engine in the morning,
-feel smooths and steady during speed up,
-the engine oil feel lighter then Castrol,
-can feel less strange sound (klik-klok) from the engine bay (my car is oredi 11 years old hehe...).
Q8 Cos:-
-take slightly longer time (1~2min) to warm up the car in the morning,
BTW i not someone the get sponser from Q8, i just tested it by my self and all the command above is just my personal opinion since i been using Castrol about 2 years and Q8 about 1years.
TQ
^_^y