How long is a piece of string?
The Oceanic routes are cheap to fly because they are fixed price, rather than per km. However, from southern UK there is a big time and fuel penalty to get you out to 16w. From Scotland or Ireland it's not so clear cut.
If you are RVSM equiped, then you should get an efficient fligh level. If you are not, you can burn a hell of a lot of fuel at Fl290.
If the French and Spanish airpace is closed or congested then T16 may be the only option, but you need to be sure that the fuel and time penalties do not outway the time saved on the slot.
However, all these are reasons why Ops may not like T16. Pilots should have no problem with it, unless they're scared of water or HF radios.
Regrds,
Norm