Sorry about the small graphs. In my next iteration of the website, I'll make the charts more legible, or have a link to the spreadsheets. Meanwhile, these charts can be compared visually pretty well without the numbers. They are all the same scale. What they show is simply how well a paper takes ink. The steps are in 5% increments for each black or gray ink. At first, I only tested the papers at 2880, but I found that some papers actually had better response curves at 1440, especially the newer papers. That doesn't mean that you can't make a good linearization or profile at either setting, but you may stand a better chance where the paper starts with a decent slope on the top black ink curve, and continues to increase to some place near the end of the curve. If the curve flattens out too close to the beginning, or even declines near the end of the curve, you need to take care to limit the ink. You can actually get the appearance of lighter blacks or reversal with more ink.
Again, in these comparisons I'm not commenting on the personalities of the papers, or my visual impressions of them, though I do talk a little about the paper textures at times, and other issues.
Lets compare some graphs, so you can see what I'm doing. From my link, take a look at the curves to the left that represent the Epson hot press papers. You can see that they achieve very decent blacks by comparison with the Moab Somerset Museum Rag (the top curves go higher with the Epson papers). That's easily seen.
Now, go left some more to the chart of Epson Velvet Fine Art paper. I only have the test for that paper at 2880 dpi. You will see the black ink curve has a nice smooth rise (except for a slight bump that may be a reading error), and reaches a dMax of 1.77 at step 17. The difference on VFA between paper white and dMax is 1.74. With the Somerset Museum Rag at 2880, dMax of 1.64 is reached early at step 12, and actually declines to 1.6 at steps 19 and 20. The difference between paper white and dMax is 1.62. Not as much contrast is available with this paper. Because black and white are relative, the visual impression of white will likely be better with the VFA, even though it's not quite as white as SMR. With respect to printing at 1440 vs. 2880, here is my take on it: If you are printing on matte paper that has some texture, you may be better off anyway with 1440 than 2880, unless you get better blacks at 2880. The detail should be just fine, and you'll have a better likelihood of getting a profile that separates the lower tones without a lot of fuss.
Aloha,
Aaron