its not a waste but going over 12GB without ECC u are asking to get file and os corruption, 12GB and ocing with what u have now would work, u may have some ram problems but 24GB is a no go. u could change to a xeon and get ecc support, then ecc ram (its the same price for 4GB sticks for ecc and non ecc) and hop that your board supports it.

what are u doing that 24GB of ram would be helpful