Welcome to the forum.
Brian will probably answer this better than I will, but here goes.
Firstly the DX6490 - I have one.
The x10 lens isgood for getting shots of birds/animals that don't want you in their space, but the focus doestake it's time and there is a noticeable shutter lag.
Now the DX7440.
Fast, x4 zoom and adjustable JPEG compression. - Sounds good for a pocket camera.
Finally the DX7630.
Only x3 zoom, (but my daughter's CX6230 is fine) 6mp - so you could do some cropping and the adjustable JPEG settings as the 7440.
I have read a few reviews on the 7630 and the problem it seems to suffer with is the increased noise at higher ISO's.
This is a problem with squeezing 6mp on such a small sensor. (don't worry most 6mp digital cameras suffer from this)
If you can wait, the DX7590 is coming, which is a mega-zoom,(maybe x12) 5mp and hopefully faster than the 6490.
Over to you Brian........