A friend has a 120Gb SSD configured as a cache with his Gigabyte GA-Z68XP-UD5 MOB. Given the 64Gb limit, the SSD is partitioned into two volumes.
The data in the "Rapid Storage Technology - Option ROM" BIOS is:
Vol 0 Raid0 (Stripe) 128K 47.8Gb Bootable
Vol 1 Raid0 (cache) 128K 64.0Gb not bootable (with one HDD is listed as the accelerated volume benefitting from this cache.)
I have the same 120Gb SSD installed with my Intel DX58SO2 MOB. Try as I might, even upgrading my BIOS to the latest version, my "Rapid Storage Technology - Option ROM" BIOS will not let me configure my SSD as a cache. Is it not possible with the X58 chipset?