Are there any real drawbacks to using a longer lens than normal for a particular format? I know print size might be limited, but if I only print 8x10, is there any disadvantage to using an 80mm lens for 35mm film, for example?

On a related note, what is the widest lens that will cover 4x5? I want to print really large - 50x40 (not on one sheet but as a collage of 8x10s) - and my enlarger won't do more than about 20x16. Another way might be to use a shorter lens like the 80mm and though it won't cover the format, I might move the negative holder around to print only the center of the circle on 8x10. This might be workable but would be clumsier than making a straight print from a large projected image.

Thanks for any ideas,
Anupam