When I get to the point of doing metrics and beyond, I'd just stop to get real food at some point, as well as take a little break. 35-40 seems to be my break point, at which no amount of gels/blocks/bars will do much to help.

For electrolytes, I use slightly diluted Gatorade--I dilute it because I hate the strong taste of undiluted stuff. Plus, adding ice helps keep it cooler. Warm Gatorade is nasty. I need to tweak this a little, because I find I'm losing a lot more salt than I think. Maybe I should look into the extra-salt shot blocks...