I was lunching with a couple of friends recently and after eating, one of them pulled out a small portfolio of color prints he had made from files captured with a Canon G6 printed on Harmon FB gloss. They were really excellent. Knock your socks off excellent!
So from an IQ point of view I would say there isn't much difference but I think the 3800 probably has a slight edge in apparent sharpness since I think the head technology is a little more advanced than the 2400.
I have a 3800 and i have had to switch transparency film to Agfa copyjet as Permajet digital negative film seemed to pool a lot, however I know Mike Ware uses the 2400 with permjet film and it prints fine, so i think there might be some difference, obviously the printer driver will not be the same with the two machines but i cannot print on permajet film even with adjusting the settings on the 3800.Kind of annoying as with the copyjet film you have to by 100 sheets at a time which is quite expensive, although i do go through a lot !