Lowe Flieger,
All bar your last line - more in a second - I think your whole post is absolutely spot on the money (pun intended).
On the last line, one of the answers will be right but as each day saunters by and more (and more...and more) detail on actual costs, schedule and capability gets explained in terms even a politician can understand I don't believe it's a simple 'lowest cost' wins.
I don't believe this is about a decision made for monetary reasons. For the MoD it most certainly is - less spent now on CV is more to be spent elsewhere in Defence. But for the bloke who will have to eat his words, he just needs a reason - any reason - to switch to the cheapest but in a way that allows him to walk back from his most contentious SDSR statement and survive.
If the sums were as eye watering as £2billion more expensive going for the CV and 5 years late on IOC, I would also agree with your summary. But they're not that stark - nowhere near as stark.
If £2billion more expensive and 5 years later (for CV) is enough for the Treasury to do a cursory 'due dilligence' review and give the PM the green light to do battle with a U-turn in the House, where is the point it isn't enough of a gap?
£1billion? and 5 years? 3 years? 18 months?
There's a point that cost and IOC delta are so close as to make a U-turn indigestible for the PM.
Then he actually has to do something he won't like - make a decision based on facts. Capability. Strategic vision for the next 50 years.
However, I actually think Cameron might just be savvy enough to do that.