Tim, I'm sorry and ashamed to report that I've found a few things that can't be done with a 2x3 Speed. But a Speed Graphic is just the thing for putting barrel lenses to good use without a lot of effort or vast expense.
Two of my impossibilities are mount and use 3"/2.0 and 6"/2.8 Elcans, both ex-F95. The lenses' barrels are too big to clear the front standard, their back focuses are too short to let them make infinity with the bellows fully compressed. The 1.75"/2.8 Elcan, also ex-F95, is another thing entirely, works just fine but covers no more -- and I'm being generous about corner sharpness -- than 6x7.
Another is use a lens much longer than 12". Imagine being limited to lenses no longer than ~ 135 mm on a 35 mm camera. Well, that's where we are with little Graphics.
Yeah, camera mutilation is always a possibility, but not yet for me.