For me, my 3 works great for iBooks and messages/facebook/twitter, but I did update it to 8.x and it does lag a lot.
My latest bitch is with the iTunes app. I was flipping through looking for some books that I don't have on it, and I got the red dot in the lower right that showed there were updates to some of the books. I assumed that the number was rooted in reality somewhere and started looking for the updates. The dot showed '3', so I found the first three and clicked 'Update' on each of them. Got 'DOWNLOADING', and moved on. Found several more requiring 'Update' and clicked them too. Now up to 5. Scrolled back to the three that I thought were 'Update'ing, and they showed 'Update' again. I clicked on them AGAIN, and they went to 'DOWNLOADING' again, and one popped up immediately 'Update'. ARG! Clicked 'Update' and went to check for other books that needed to be 'Updated'. I found SCADS of them! I assume that most were not on this iPad, but who knows.
Feeling defeated, I clicked on a book I had started on another iPad and it downloaded the book in like seconds, and I started at an earlier part of the book than I had left it on the other iPad (ARG!) but kept reading...
I'm wondering what the heck is 'updated' on an ebook? Why does iTunes app have such an issue with iBook updates? Why do I continue to waste my time with it...
Whatever...
I will keep my 3 until it goes tits up and is scrapped. At least, HOPEFULLY, it will run iBooks for a few more years...
Re the idea of an iPad 'Pro': They had better put some muscle under the hood of one if they want to keep people invested in the iPad line. They shouldn't scrimp on the horses, or the stalls, if you catch my meaning...