Hi KWoNi (kwoni) , cutting thru there is not really saving much piping but it will make your room nicer. the shorter the piping runs around the room, the nicer your room will be.
for the 2nd option, is actually what is shown inside my first picture which i took from other people house. the whitish is the toilet and the dark brown thing is the air con ledge window.
no matter where did you put your master bedroom aircon unit, your bedroom 3 air con unit piping need to go thru master bed room then thru your aircon ledge.
this picture shows the posible option that you can run your piping.
for the 3rd option, you cant go thru the wall just below the beam as you might hit the electrical wiring.
all electrical wiring (HDB hidden wiring) comes down from the ceiling - which i had clarify from
the service centre room (blk 488 level1).
we had a hard time doing the laying plainning as this way cant that way cant. sigh.....