Hey Stephen
There is a great discussion of carbohydrates here:
http://www.medioncorp.com/the-science-of-e-load--p136131There is some discussion about 'slow vs. fast burn carbs', and their choice of easily digestible carbs.
Looks like FLY is maltodextrin only, and eLoad has dextrose also.
You may want to mix these in your MEGA bottle. You can add more calories with the FLY without adding sweetness. You'll have to be very cautious to have enough water, or the carbs won't be absorbed, and you'll simply get 'sloshy' and bloaty. Not good.
When you are doing your shorter races, I think Eload, in the regular formula would be good. It has the right % of sugars to be properly absorbed, with the mix of dextrose and maltodextrin.
So, I didn't really share anything new with you, but have another read of the info at the link above. It does a better job of explaining this stuff.
Ginny