In a new attempt to make classification even harder- I introduce the category of spokes!
I did a quick search of posthumous coins that I have sold recently and found 4, 6 and 8 spokes.
Since more is usually better, I declare that 8 spoke quadrigas must be the rarest and most valuable...until an example with more spokes is found. ;D
Wait a minute...is the six spoked example actually a Christogram (see last picture of iota chi)...they are definitely the most valuable now!
Looks like I just have the 4-spoke variety. As long as it still gets me to Heaven...