so you got too much performance/good FC and want to lower that by going for thicker EO?

why you want to change to xw-50 oil? is it because want extra protection? or.. you expect that it will give quieter noise? or.. the foreman keep asking you to take xw-50?

try different brand/model of lubes, not thicker viscosity.

Try Penrite 5W40 HPR or their premium range. Confirm will reduce lifter noise. Don't know how it does it.

Engine gets rough with mc3 at 5k km.....no good

It's good la. But how good it is , really it depends on preference. My Wira ran quite well on Amsoil but was quite rough with Mobil 1 Gold. My current Nissan runs very rough with Prince but runs great with Penrite. Right now I'm running on Penrite HPR for all my cars.
Can la. Not gonna kill you if you go with 15W40. Your engine is probably leaking somewhere anyway. Better than running zero oil.
My preference would be (Mind you.. personal preference)

1) Shell Helix
2) Elf Evo
3) Repsol

I've used all except the Elite Evo Repsol. I've used the formulate elite or whatever you call it from Repsol, the semi. Wasn't too happy in my Wira. Broke down pretty fast. But just a note, my Wira wasn't stock so the requirements for the car probably was a little more demanding than a stock wira. So perhaps I probably shouldn't have used a semi.

Where did you get your oils from at that price?