I think for 243, putting the DDs on 199 to 243w crossovers will
be better. Then the DDs will only serve 243w down trips in AM peak,
but the rest of the time operating S shift on 199.
The present 199 DDs aren't full to the door, but at least they have
more loading than the DDs now on 243w! 
And also putting more DDs on 199 will let SBST compete better with
SMRT's 172 for people staying along Jalan Bahar... 