what oil should i use!!!!!

[cable tie]

Oh i probably opened a can of worms with this question, however i noted some foccers buy car spec oil, and whilst ive been tinkering with cases and now need to fill the engine up with oil, i have afew options.

bike spec comp4 10-40 semi syn £39
bike spec comp4 10-40 fully syn £47

car spec mobil one 10-40 semi syn £29
car spec mobil one 0-40 fully syn £26 (special offer in halfaurds)

Now in the past ive always put comp4 semi syn however if i can buy the same product but cheaper than im game

so who puts what in the engine and would you recomm fully syn!! bikes done 12k


THX Dave