I've found that I can manage a 5 mile run without extra sugar, as long as I start out above 6. If I'm lower, then I'll drink some fresh orange juice before going out. Although my sugars hardly change after 5 miles, I have found that I'm at risk of hypos up to 24 hours after, so will probably start reducing my insulin after a run for the next 2 or 3 jabs.
When I did the Great South Run recently, I hadn't trained above 5 miles with the diabetes so wasn't sure what would happen over the last 5 miles. I ate a few jelly babies and kept well hydrated and that seemed to do the trick. I started the race at 11.8 and finished on 5.8.