@James-
Dangerously close to thread creep here so I'll keep this brief and leave it there.
What I guess I'm asking is whether its worth doing 7 years with BA and then looking elsewhere for a faster route to command.
If you want to live in Europe, the answer is probably no. Very few people ever choose to leave BA simply because they offer some of the best terms and conditions around. If you did choose to leave, don't forget that other airlines in the UK are unlikely to offer you a direct entry command - you'd have to start again as a junior FO and work your way back up.
If however you see your long term future in the middle east or far east and have no intention of coming back, then I suppose you could choose to leave permanently if the offer of a direct entry command came up somewhere. But I suspect what you will come to realize is that your overall working conditions and quality of life matter much more than which seat you sit in. Command is obviously desirable, but it certainly isn't the be all and end all. This is particularly true in airlines like BA where seniority is king. As a senior first officer with good seniority on your fleet you can pretty much write your own roster. As a junior captain you cannot. Hence why many people deliberately delay their command or never bid for it at all.
Edited to say: I agree wholeheartedly with FullTanks. If you're already talking about leaving after 7 years because a fast command is more important than anything else, this probably is not the scheme for you.