90/90 is enough for YBR.
It's just a 10 BHP bike.
100/90 even puts burden on GS150. After trying it on my GS, i replaced with 90/90.
Many go for 100/90 on GS because its front brake is weak and they try to make up for it by putting bigger tyre at rear.
No such issue on YBR as it has got that nice disk brake at front.
That leaves only cosmetic reasons. If you are putting it on for looks then no argument there....