Thomas, good luck on the fast speed. You are trying to copy what eje67 did -- here's his trip report: [url=Main Mount Whitney Trail, 7/8/14 solo day hike]Main Mount Whitney Trail, 7/8/14 solo day hike[/url]
I did the hike in similar times about 30 years ago, and I attribute it to being in really great aerobic shape. I ran 3 distance workouts (about 4 miles) a week: once a week ran laps around the outer rim of a football stadium, including climbing above the stands on each side, descending to street level at each end; once a week included some weight training, then running six flights of stairs 12 times -- maxed out aerobic conditioning. I could run a 6-minute mile back then.
You can read my comments about the water in that thread. Take at least 3 liters from Trail Camp. Bob R hides one at Trail Crest for the trip down. Use bottles so you know how much you have left. Suck on candy (I like Everlasting Gobstoppers and shot blocks) to help the dry mouth.
As for food: Take granola bars, trail mix, shot blocks, candy, maybe sardines in oil (with a flour tortilla is my favorite). Peanut butter and jelly are hi-calorie (again with a flour tortilla). Every hour, eat a snack and drink about a pint. The altitude may kill your appetite above the switchbacks, so be sure you eat lots early on. Electrolyte tabs really help too.