Jack, I agree with most of what you say, having now used both the 4000 and the 4800. I would suggest as follows: the decision really depends on the intended usage.
The colour gamut is a bit better on the 4800, but the difference isn't a knock-out one for colour work on matte. Anyone just using it for printing colour on matte papers should probably not make the up-grade unless the cost difference is really minor.
The 4800 prints more neutral blacks and handles coated media better - at the cost of changing the inks. So people who make alot of B&W and alot of coated media prints would probably find the 4800 advantageous, especially accompanied by ImagePrint with Phatte Black ink, according to Michael's review results (I haven't gone that step yet.)
So far, I am also finding the 4800 uses less ink per print, clogs less frequently and requires fewer cleaning cycles to de-clog than was the case with the 4000. The main qualification to this finding is that I've only owned the machine for a couple of months and made about 450 prints with it - not enough of a track record to come to definitive performance conclusions of this kind. Several months from now, I may write more about this.
