I've got exactly the same problem as the OP!
10" is not too bad but too small for PDF A4 size academic papers .
I've already got a 10" dell mini so I can tell.
I see all the tablets which have appeared on the market and that doesn't suit me at all... Of course you can zoom on the go but I don't see that as completely comfortable to have to zoom in, zoom out, back and forth constantly.
the diagonal of a A4 size is : 14,33 inches (basic calculation

), so it's the size that you need. But problem... I've found for the moment no ultraportables with this size, or at a price very high.