51m
I think it's important to note that Grimmjow in Resurreccion is presumably a lot faster than Askin and Urahara.
Obviously, Grimmjow has always been super-fast--his first fight was him outmatching Ichigo's Bankai, the transformation that turns Ichigo into a Speed Demon--but for this fight specifically, Urahara needed to find a stretch and then speed along as fast as he could to evade Askin's attacks, while making sure that Askin never turned around to see the Panther King sprinting along the trail for the killshot.
That means that Grimmjow not only had to be fast enough to keep up, but also to close the gap before Askin became aware.
