Um, correct me if I'm wrong, but I don't think that the experience of a 5k race in heaven could possibly be any better than one on earth.
Running is a chance to experience heaven on earth. It doesn't matter whether you PR or have the worst race of your life. The point is that you get to be out there, competing, finding your body's limits, breathing the fresh air, etc. There are no losers, only winners and non-winning competitors. Do you think Alan Webb is a loser because he came in 8th? No way. His life is f***ing awesome. He gets to run for a living. And next year he'll get to represent his country at the Olympics. At the same time, Webb not being a loser doesn't mean that Bernard Lagat can't be a winner.
I guess if running in heaven were different, it would be because people wouldn't be so hampered by excuses, jealousy of people who beat them, or other negative feelings related to running. In heaven, running would only involve the good stuff.