Points to ponder, the flying hours in the B744 F/O job don't count for much in the long run, only towards total flight time, not really a factor. On the other hand Command time is gold under any circumstances and particularly when you next need to look around, a redundant B744 F/O will spend a lot longer on the heap than a current captain. Don't fool yourself, in this day and age you could be redundant within a couple of years of joining ANY UK company.
An old skipper, sadly now passed on, told me a long time ago that a command on anything was better than an F/O on anything.
He was right, you have no dilemma, go for the command.