I've been testing all my fountain pen inks on a variety of papers--you can see more results on my Flickr page, and on the discussion on Russ Stutler's Sketching Forum--last night was fun, I was having a three-way discussion in as many countries! The 'net is an amazing place...
You can find some of the samples, mine and others', here:
http://www.sketching.cc/forum/viewtopic.php?t=1353 And the discussion here:
http://www.sketching.cc/forum/viewtopic.php?t=1159 that someone else started, testing different inks.
It appears paper and the sizing DOES make a big difference, but its not the whole answer...
vickylw and I have tried the same inks on apparently the same paper (Strathmore 400 CP) with quite different results.
Go figure.