For the most part, an end user should ignore the amount or type of cache as a selection criteria.
L2 may be associated with individual cores, while a larger L3 might be available to all of the cores.
The motherboard has no part in this. It is a cpu specific amount, and will vary by cpu model.
It can not be changed.
Look at the bottom line for cpu effectiveness.
One simple metric might be the passmark number.