Hi there,
If I were you I would choose for Y, because it's such a short flight and before you feel comfortable, you are arrived. On airliners.net you can find a trip report of someone who travelled SIN-CGK-SIN on KLM's WBC. Here are the links:
SIN-CGK
http://www.airliners.net/discussions...ad.main/39576/
CGK-SIN
http://www.airliners.net/discussions...ad.main/39664/
somewhere below you can find pics.
Maybe that you can find some information here.
I wish you a lot of succes!