I have flown NCW often and First a few times - as I am not over 6ft tall I have no problems with the NCW seat. I think that the NCW product is very high quality and this makes the upgrade to First decision harder - when it was the old cradle seats - well that's another story.

To me the difference is in the absolute attention to personal service that you get in First, the better food and drink, and the spacious cabin. I don't think I would pay the extra £2k though - but if I had paid £3.5k for NCW - and I had the miles I would certainly use them to upgrade - then use the extra £2k to buy a few nights in a really luxurious hotel at the destination.

There was actually a fairly lengthy thread on this subject a while back so it might be worth trying a search.