I'm facing the same question. If the role of the D2X is a APS-C sized sensor and backup to the D3, then wouldn't a D300 be a better choice? Other than the ruggedness of the body and 8 fps in high speed crop mode, I don't see any advatage for the D2X. I should be able to get a D300 and have a little spare change for my D2X (hopefully). Since all the bodies will depreciate like a PC, it seems selling it while it is still worth something is better then getting "stuck" with it after it is fully depreciated down next to zero.
Does anyone think the D2X is worth keeping as a better backup to the D3 over getting a D300?
Good judgement comes from experience, experience comes from bad judgement.~ Mark Twain