Sub-Pixel density (RGB) = {[(3*X-Pixel)^2 + Y-Pixel^2]^1/2} / diagonal length
Sub-Pixel density (Pentile) = {[(2*X-Pixel)^2 + Y-Pixel^2]^1/2} / diagonal length
This would give iphone a sub-pixel density of about 613 and Galaxy Nexus about 414. This is more than sub-pixel density for GS2 which is RGB.
If we talk about sub-pixels, we also ought to consider that each individual sub-pixels can be addressed in Pentile. The image is rendered at the sub-pixel level, and in case of RGB it's a the pixel level - a complete set of 3 sub-pixels is the minimum addressable entity. Also to be noted that it's only on horizontal axis and no changes on the vertical axis. The main problem with Pentile is how the sub-pixels are arranged. Sub-pixel elements are placed diagonally whereas in a RGB they are in a straight line. Due to this diagonal structure, the lines sometimes appear blurred. But those won't be a factor as the resolution increases towards HD or higher.
But it has advantages too. They are thinner and production is more efficient. Pentile generally gives better battery life.
That's awfully big text, of course you're going to see less jaggies when the text is bigger. I want to see smaller text, like a 100% zoom view of the frontpage of nyt.com.
Fair enough on the calculation, I merely did the quick math to compare how many pixels there are, and pixels = sharpness. Although as I've not seen or used any high res pentile screen in person, I'm in no place to judge if it would be noticeable.
Didn't know that about the sub-pixel addressing either, but it doesn't seem like it helps.