This is easy to calculate. Below is a comparative chart of my running and joggling PB times and the percentage differential:
400m: 53 secs. vs. 59 secs. (89%)
Mile: 4:22 vs. 4:49 (90%)
5K: 15:05 vs. 17:50 (84%)
10K: 31:59 vs. 36:27 (87%)
30K: 1:43 vs. 1:55 (89%)
Marathon: 2:30 vs. 2:53 (87%)
Joggling pioneers like Bill Giduz say joggling should cost you only about 10% of your time. Mine are a bit higher, but that is likely due to the fact that most of my running PBs were set about five years ago when I was a) younger, b) fitter, c) 8 lbs. lighter, d) less overworked, e) less sleep-deprived.
So I think the 10% figure is about right, and it may be even lower, based on yesterday's 35-minute non-juggling 10K. My running speed is slowing down over the years, but my joggling technique has improved greatly, as have my props; the lightweight Sportballs have made a huge difference for the long-distance events.