thanks everyone
your responses have been very helpful !
i think the most logical course of action is to finish off this year with UA and re-qualify - and then come january, will consider whether staying on or switching to KF or OZ makes sense. if i switch, one plus point for KF would be that discounted SQ flights would still give me credit which i cant get now on UA
but will look into OZ abit more.
also yes - my math is quite bad
oops !