Another thing to consider is the 2 screens. I find it useful for technical documents to have 2 different pages open at the same time. (for checking references, equations, etc).

Does Ipad has common space? Like in android you can open the same pdf from different programs. It seems from my experience with the iphone that each program has its own space that can't be accessed by other programs. This is certainly annoying.

Anyways if you are not interested in 2 screens and having eink then you should also consider the HTC flyer rather than the ipad