I use an iPad with unrealBook as the music app. I've been using this setup for
~3-4 years or so. I am eager to see if Apple will introduce the rumored 12.9" iPad.
For my eyes, the iPad (9.7 inches) is "barely big enough", but for more complex music (with "more on the page"), it's a bit small. I have taken many hundreds of PDFs and re-done them (using Photoshop) with larger chords and lyrics, which helps a lot. My band uses iPads, and we "sync" them together with unrealBook's sync features, so when I turn a page, the whole band all see the same song or page.

This may not work for everyone, but so far it's been good from my perspective ...

-Jim