Wearer of Vaporfly's wrote:
Spikes are faster for the track. The 4% are marathon shoes. This puts her at 29:55 IMO. The shoes are not grippy at all.
The 4% shoes are best for the 10k. I've experienced it. In the marathon and half, the bounce is gone after 10 miles. I've seen unreal 10k PRs with the 4%.
You could put some hex-head screws in the soles for optimal traction + bounce.