It seems to me that the Spartan-C we got in canon is a bit of a missed opportunity. The first khan of the Ice Hellions, Stephan Cage, canonically commanded the SLDF's 200th Dragoon Regiment during the Amaris Civil War. Dragoon regiments, in the SLDF's system, were heavy/assault 'mech units...but Cage's command was still somehow "used primarily for reconnaissance..." uh, whiskey-tango-foxtrot, over?
Well, between the Spartan and Lancelot, it turns out the SLDF had a couple of appropriately-chonky machines that were still able to keep pace (at least on the ground) with the low-end mediums and lights that most other militaries of the time would be using for skirmishing or picket duty. Given the SLDF's penchant for equipping entire companies or battalions with the same chassis-type, I wouldn't be surprised if these designs made up the bulk of Cage's unit. At the very least, he almost certainly would have been very familiar with them.
Then, upon his accession to command of the Ice Hellions, the Spartan's high speed and likely-prior association with their khan makes it a great candidate for an Ice Hellion early totem, particularly since the Hellions invented the lighter clan version of MASC, and I don't see any restrictions on clan machines using superchargers as well. That gets you a respectably-armed and -armored 80-tonner moving 5/8(13) - an ambusher's dream (if unfortunately prone to locking up and falling over)! Definitely fits the Hellion doctrine of "striking first is more important than actually winning."