Well, I don't really know for sure which one is the better sustained turner, but when it degenerates to low speed, I'd guess the Pony. It's nice multi-angle combat flaps can make the difference here, and I believe will give the Pony the edge.
However, neither fellow really wants to be in that position, least of all the Pony driver since the D9's accelleration is superior. Where the pony will use that low speed handling is in a horizontal rolling scissors, I'd bet the Pony will kill a D9 in that move once things get slow enough.