I must admit, I find maintaining 11.5kph even for just 10 mins at the end of the 30 min run pretty tough. (Sure 20 mins will be a lot harder still, to get to the 40 min total time I'm aiming for now).
Of course, many years ago I used to run 2 hours at a time for 12kph but I was 11.5 stone, fit as a fiddle and much younger, and hadn't smoked as many fags (or eaten so many pies)
I think I'd like to eventually manage the full hour at 11.5kph, but reckon that's some way off right now. One step at a time etc.
Maybe, just maybe I can recapture my old V-taper body shape - but I reckon Mrs C is going to have to stop making me all my fave dinners for that to happen, no matter how hard or long I end up running/training