Close
I looked at the information stored in both my TIFF and PNG scan:

TIFF: http://img161.imageshack.us/img161/2261/screenshotosx22zf8.jpg
PNG:
http://img246.imageshack.us/img246/4199/screenshotosx21ch2.jpg

And so as to understand the information, the specification of the TIFF 6.0 format:
http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf

From what I understand of the spec, most addition in the TIFF say that it's a 24bit RGB picture. Nothing much that is better for resolving color problem. Other than that, both store the ICC Profile which is the real deal for color.

For the time taken, yep it's longer but I'm a bit limited by storage space ( laptop ) since I need to leave some free space so as to prevent free-space fragmentation ( bad for my swap )