The higher the octane, the slower the burn rate, typically. White smoke is water, so it may be old/contaminated fuel in their tanks. I've never seen any race cars spit anything running leaded race fuel. It should color the plugs some and the inside of the exhaust pipes should be a light gray when running leaded fuel. The toluene in super unleaded creates soot and will turn the inside of exhaust pipes black.
FWIW - E-85 isn't available everywhere. Closest from here is 200 miles, if they even still sell it. A few people around here tried it, liked it, tossed it because it's just too damn hard to get or keep around. Might as well buy VP M1 and mix your own. The drought killing the corn crop and the reduction in subsidies may make that stuff dry up like spit on a Texas sidewalk, and drive the price up too. If I had to run 110 or 112, I'd buy VP in 54 gallon drums to reduce my costs.
1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
Owner built, owner abused.