No matter what you do with the cache file you won't see a difference with the setup you currently have. All your drives are over 50% occupied and that will give you a serious hit because the Master file tables are going to be huge. Consider a RAID 5 setup or even a RAID 0 setup if you do frequent backups. All Raid systems need at least 4 drives to get the most bang for the buck.
My 2 cents
-James
I second Jame's motion. Your drives need to be larger, whether via a RAID setup or simply purchasing new HD's. Memory is getting relatively inexpensive, purchasing 2TB drives would be a huge benefit and simple remedy. RAID setups are faster than individual drives.
I would also recommend deleting old LR backup catalogs, they become a memory hog if allowed to accumulate excessively. The older ones serve no purpose, how old is up to you. I would also recommend putting the cache files on one of the data storage volumes (Pics and Personal) instead of the Boot. I set my catalog in Lightroom at 100GB as I have plenty of room, but you don't want another memory hog on the boot. Use the Boot just for systems and applications (probably under 40 GB for most of us), as Lloyd Chambers would say, it is better computer hygiene. Chambers does recommend keeping the Catalog on the Boot, btw.
Another great way to go is purchase a SSD for the Boot. You will love the increased speed! If you have a Boot dedicated to systems and applications, a 100 GB SSD is plenty. The nice thing about SSDs is they can be near full and still run just as fast. My 100GB SSD Boot has over 60GB available space, and I do have a ton of Applications.
