I run cane Creek Crosstops on 'cross and MTB fitted with Midge bars. You want the 26mm clamp. Fits fine-- there's no "fudging" about it.
Awright is correct in saying that the drops is where you'll need to be 90-percent of the time. However, I too like some variety and like the in-line brake levers for general noodling around and sometimes it's just convenient to have brake levers up there!
I race 'cross and LOVE it but my bike is not a "pure-bred" race-only machine. In the off-season it gets a bottle cage and it goes up on the same trails I ride the MTB.
As for how high for the Midge bar-- I'll add my 5-cents worth. On both my bikes, the tops are about 1 inch higher than my saddle. And the drops-- the sweet spot-- is a couple of inches below the saddle. About where my hands would be on a conventional flat-bar setup.