You can't really decouple the movement curve from the available pod space.
Case in point, I also would take the Grendel as first choice, but my second choice would be the Shadowcat, since I like jump jets in general and favour being able to jump out of a bad situation, which the Ice Ferret is not able to do. Plus, the Shadowcat can match the running speed of the Ice Ferret for a short time if needed, thanks to the MASC... and you don't usually need more than one turn of active MASC to get into position or out of dodge at these speeds. The lower base speed gives it more podspace to play with and usually a bigger punch than the Ice Ferret.
But if we are talking about more(or rather less ;D) than just 45 tonners, I'd take the Viper(Dragonfly) over any of them in a heartbeat. Imho it is an Ice Ferret done right, at only 40 tons no less! ^-^
It pays for that in BV however, compared to the Ice Ferret. Most of it's configs are quite a bit higher in BV than those of the Ice Ferret, and come close to the Grendel's BV.