The only times I really use the iPad in place of the Kindle is when I'm in a dark place (I've used it quite a bit outside at the hot tub at night), and I use the iPad for Instapaper usually instead of the Kindle.
Another reason I prefer longer reading (which Instapaper doesn't really fall under, while articles are usually longer form it's not like it's a book) on the Kindle is because with the iPad I find that I'll be too easily tempted to press Home and mess around with something else (I realize this is my own fault and not necessarily a fault of the iPad, but it's something that I'm sure other dual-owners have experienced).
Yes, how many times have I earmarked papers only to find myself web surfing or playing games? gah...
There is, however, a surprisingly major difference (at least to me) which is highlighted by this microscope comparison: Dot pitch. The iPad's IPS panel has a pretty average dot pitch, but I was surprised to see that the Kindle's e-ink display has essentially none. Even though the eye compensates for dot pitch, I have to wonder if that still might make a difference.
So, to say that using a Kindle is more like reading a book than an iPad strikes me as bogus. I don't understand how a backlight or not decides an item's bookishness. Certainly, neither has pages.
Anyway, there are many reasons why the Kindle is more like reading a real book besides the display that looks identical to a piece of printed paper. First of all, neither books nor the Kindle have a backlight which does, in fact, make the Kindle more simliar to a book than an iPad despite its lack of pages... You can read a Kindle on the beach or on a deck in the brightest sunlight you can imagine and the screen will just look better. The same goes for a real book. Just try that with iPad with a backlight and you will see a difference there.
Also, due to the lack of backlight the Kindle is much better suited for reading before sleep just like a real book. The backlight of a computer monitor is the reason computer people struggle with falling asleep. A good fiction paper back is the best sleeping pill in the world and you just can't get that effect with a backlight screen.
Finally, just look the article we are commenting on. Do you not notice how similar the Kindle character is to the newspaper, magazine, and book characters at 400x? I would dare sare it is sharper.
I use my kindle on my boat. 99.9% of the time I'm sitting in the sun reading it. I can do that with a book, and I can do that with a kindle. The iPad or anyother backlit screen is just not an option. I can barely see my cell phone or camera screen on the water, but I read the kindle becuase it is a fundamentally different technology.
I am curious if the kindle, in your use case, will- at the end of it's life- have distinct hand-prints where the original color is intact (if not physically smoother).
"The iPad measured at 6.2% lower reading speed than the printed book, whereas the Kindle measured at 10.7% slower than print. However, the difference between the two devices was not statistically significant because of the data's fairly high variability. Thus, the only fair conclusion is that we can't say for sure which device offers the fastest reading speed. In any case, the difference would be so small that it wouldn't be a reason to buy one over the other."
Also, that study wound up being based on 24 subjects reading for about 17 minutes. Hardly a comprehensive test.
Really it comes down to personal preference.
Reading speed is not all I care about. In fact, I don't care about it at all, really, so long as it's within acceptable limits.