I have always used Motul 5000 10w40. on all bikes below 4K miles.
But the bike is now past 5k so this time i switched to Motul 5100 10w40 Ester.
It's a semi-synthetic with added esters that has always given good performance and value for me.
As long as the JASO MA2 is on the can, it is good for the wet clutch type that the SX uses.
I have never known a clutch to slip on a modern bike when using fully synthetic (as long as it is labeled with the correct rating JASO MA2).
However i did once have a Suzuki Bandit 1200, one on the early ones that had only 1.5k miles on it. I put in fully synthetic and found it ran really hot, so i changed the oil to semi-synthetic and the problem vanished. I have always surmised that because the engine was still tight and new it needed to wear in some more before using a fully synthetic oil.
I am not an engineer and cant claim to know a lot about oils but thats my tuppence worth, take it or leave it.
P.s Busters motorcycle accessories do it for £35.95 for 5 litres.