Interesting, I just realized I had the stock 32MB CF card (forgot all about it) so I decided to compare it to the SanDisk Ultra 256MB CF card I have. The unscientific results are below;
3 different pics on each card at 2560x1700 (3:2 ratio)
Nikon 32MB CF card: 8 to 9 secs.
SanDisk Ultra 256MB CF card: 3 to 4 secs.
Looks like the Ultra was a good choice for my 5700 :-)