I'd have said join BMI DC.
With two flights per year in C all the way to NZ or S.E. Asia, even at 1.5x rate that should be enough to earn you *A Gold status and easily renew each year.
Redemption rates will be better with DC than KrisFlyer and earning potential will be even better if you get to 55,000 miles per year which I think you will (after the first year).
*A Gold will give you the same benefits as KrisFlyer Gold*, and I can't see you getting PPS status so you won't miss out on anything there.
Also, KrisFlyer has a 3 year mileage expiry policy so you use them or lose them. DC miles don't expire as long as your account remains active.
*although you won't be able to earn miles from onboard duty free purchases.
DC also has the benefit of earning more miles from UK based activity (e.g. credit card use).