Another upside to 5x12 is that a LOT of lenses for 8x10 will cover 5x12. I've got a number of fantastic optics to fit it. From widest to longest:
159mm f12.5 Wollensak W.A. Raptar - covers, with limited movement, gets soft in the corners pretty fast, but with a 159, who needs movements it's so wide!
210 f6.8 Graphic Raptar - another wonderfully tiny lens with huge coverage - I can apply full rise on my 5x12 and not run out of image circle.
250 f6.7 Fujinon - it covers, with not a lot to spare, but it covers, and it is much smaller than my big Nikon 240, so it travels well.
300 f6.3 Commercial Ektar - what a great lens. 'Nuff said.
I dream about getting the Nikon 450m to use on both the 5x12 and the 5x7.