engine oil for gixer 6 k2

I want to replace my engine oil and filter for my gsxr 600 k2, i recently had a 7000 mile service from my local bike shop and he used castrol 10/40 motorcycle oil.
One of my mates said i should be using fully sinthetic, when i asked the guy at the shop he said that that full sinthetic oils will make my clutch slip.
i want the best oil and filter for my bike and dont mind paying extra for a k&n oil filter to go with. I,m confused now… HELP please :|

Waste of money just get 10/40w semi with a suzuki filter

Waste of money just get 10/40w semi with a suzuki filter

indeed 10/40 semi and regular filter, thats what iv always used on my GSXR and it now has over 40k on the clock…

and don’t buy expensive oil, Halfords oil is fine, all I ever use:)

so why do they use fully synthetic oil when racing ???

maby cose they dum or summit :slight_smile: