sorry if this sounds harsh in advance...
but if you think that there is more than one route from LHR then you better brush up on your company background info...
as cx is a hong kong operated airline, most flights will go through the hub (HKG) and there are almost none that has an onward journey. but yes there are 4 flights / day indeed so you may fly more than you think...
more so, i am not entirely sure how they work it within the company, but they may a e.g ask you to fly to hk then go on to another destination. but if thats the case whats the point... you may as well live there!
also, the UK tax more, i doubt they will change your salary... and you are unlikely to get any allowance! which im not sure if you get in hk...