First time I've seen it Avios being less value in business than econ (not that I've been looking that hard):
SIN-HKG on CX:
Econ 20000+GBP63 or GBP1281 = 6p per avios
Biz 40000+ GBP 63 or GBP1947 = 4.7p per avios
Both ticket prices seem excessive considering a Tiger Airways flight can be had for GBP170 and its only a relatively short flight but check two dates in April/June same price.