I used 2 8x10 sheets of film just to test my 8x20 camera after it was complete (light leaks and such).

If you tray develop you will get some additional edge density at the seam that wouldn't be there on an 8x20 single sheet. I'm assuming you will process the two sheets like normal 8x10's.

It's the same additional edge density you normally get on 8x10. I suppose it depends on how picky you are.