Re eating and races, my BG sometimes seems to run up before races. I'll correct but take cut corrections, like 1/3 the amt and then run with IOB, not my favorite scenario but, the advantage at races is that there's Gatorade stations every couple of miles which usually makes it easier to jack my BG back up when I run. I've found through running that it seems to take about 8-10G of carbs for 3ish miles so, if I'm doing a 5K, I'll have a glass of skim milk and run. 10K, I'll have something before I go and about 1/2 way. This usually works but, if I get into a flow or whatever and my BG runs down, I have something with me to snack on, pretty much always.
The other thing I do before races is to try to eat pretty early, like 4-5AM for an 8:00 AM start. That gives time to get most of the insulin cleared out. It's always a weird time of day with DP and adrenaline going on so it pays to test a lot although I "cheat" as I have a CGM which is also very handy. I've run into a couple of other D runners and seen them run their BG up to 300 and just plan to "run it off" but I don't do that, ever. In Chicago 2012, I ran up because I was low before the race (opposite of what I just said...), ate some stuff (luna bars, 110 at 3 miles, had gatorade and then my BG was high (up up up to peak at 190ish on my CGM, the line is on my Tu homepage here...) for like the next 15 miles or so, when it finally broke I blew it and full dosed, instead of cutbolusing for the Gu packet so then the last 8ish miles were exciting and I had most of the fuel stops to cover the insulin. I finished at 68 or 73 or something but they had carby 312 beer and potato chips so I was ok with that too. The best thing to do to find out is to test and correct but don't do full corrections if you're high and running. Run a few miles and test again. It's easy to get caught up in chasing time and not wanting to slow down to test but it will make you a stronger and, maybe more important, smoother runner so you can have a better race. It's funny at the end of the race when you slow to test spectators go "c'mon run you can do it..." but then you pull out a meter and they're like "oh..."