If I was in your position and the $1400 wasn't going to impact anything and was money to burn, then I'd do it. Otherwise, it is probably not worth it.
Without a doubt I prefer the 4000 as the layout makes it seem FAR more spacious then the 3900 and the forward galley is part of that and an awesome feature. Access to the bow is nice as well. But I'm not sure its worth paying extra.
What you might be able to do is as you get closer see about negotiating a lower cost for the upgrade - even now, you might be able to get them to reduce it a bit.
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