You have to ask yourself - how much will the old 5d drop to?
Between the old 5D and a new D300, without nikon glass...
Of cos the 5D will drop in a little in its price tag, unless a 5D MkII was release then the price of 5D will drop alot.
Also 5D win hands down for image quality due to the fact tat it is a FF body.
Other thing else, D300 is comparable in pricing with 5D, or even lower by the time D700 was release, not to mention D300 is in its own class.