Hi Bill
I think you are spoiled with a large 12.1 screen in portrait mode as I am spoiled by my laptop on it's side with a 14.1 screen.
I have tried viewing music on an ipad and it doesn't really come close to my liking it. In a pinch I could use my 10.1 Asus android if I placed it over my screen on my T4 as I know some do but there goes on the fly use of any screen buttons ect.
Really, for using lead sheets anything be it a laptop or a tablet in landscape mode is not going to be desirable again for anyone that is used to a large screen in portrait mode.
I have been waiting for something bigger to come out in a good price range. The only thing I see rather recently is a 13.3" Hannspree android tablet. In portrait mode it would be as close as we could get to a regular piece of sheet music. The measurement for the width of viewable screen space is 7.5" which is about what an 8.5 x 11 piece of paper would be if you figure the margins.
The resolution is better than your MPP and my laptop. It has Bluetooth so if you ever would want to hook up a wireless page turner you can do it.
MobileSheets is a developing app that seems to be the go to android app for music. I have been in touch with the developer and he is adding where you can use the tablet to set up your keyboard or use your keyboard to open the pdf all at once instead of picking your lead sheet and then setting up your keyboard. What a time saver.
The Hannspree 13.3 has had pretty good reviews. Also, I found out how popular it is becoming with musicians as the gigeasy stand mount company mentions on their site that the Hannpspree does not fit on their holder. Interesting that they singled out that one and none of the other 13.3's, which there are a number out right now also would not fit their particular holder. In other words, gigeasy is apparently being flooded about questions regarding this particular brand of 13.3.
https://thegigeasy.com/product/mic-stand-mount-universal/And to top it off, until now it was retailing between $250 and $300, and now you can get one shipped directly from Hannspree on Amazon for $200!!
http://www.amazon.com/HANNSPREE-13-3-INCH-TABLET-1280X800-ANDROID/dp/B00FA9ACIG Each company and app has their pros and cons. But I know that for those that want something in portrait mode about the size of an actual hard copy a 13.3" is the best solution that I can see at this time, especially for the money.
Definitely worth checking out even if one just tries it out and would happen to decide to return it for some reason.
Hope, this helps Bill.
ScottL