The N9 has quite large bevels compared to the current crop. So even a 4.3" screen might fit in the same physical dimensions. But I agree the phone itself shouldn't be larger. I'd prefer a smaller device, like the N9, which packs a punch (inb4 "that's what SHE said!").

As for ARM vs x86.. I must say, with Linux I can hardly care. Cross-compiling seems trivial these days and the lack of proprietary software makes the difference even less significant, software-choice-wise.