I want to build a MariaDB server.
I am researching DB performance according to CPU specification before server purchase.
Are there any benefits to gaining as CPU Cache changes from 8MB to 12MB?
Is it a good option to purchase a large CPU Cache?
No.
Don't pay extra for more cores. MariaDB essentially uses part of only one core for each active connection.
Don't pay extra for faster CPU or anything else to do with the CPU. If you do become CPU-bound, then come back here for help with optimizing your query; it is usually as simple as adding a composite index or reformulating a query.
Throwing hardware at something is a one-time partial fix and of low benefit -- a few percent: like 2% or, rarely, 20%.
Reformulation or indexing can (depending on the situation) give you 2x or 20x or even 200x.
More RAM up to a point is beneficial. Make a crude estimate of dataset size. Let us know that value, plus some clue of what type of app.
SSD instead of HDD is rather standard, but that may give noticeable benefit.