There is no real distinction between the two lines it seems (to me). But I do notice the DX seems to have better lenses and speed. Also the price reflects it.

Let me share that I enjoyed my DX6490 on an 8 day trip and it performed very well. If the 7490 or such is a significant stepup, I may consider it sooner than later.

The one thing I learned was to pop open the flash when in doubt.

Bob