Hard Drives / Cache Drives

Hi all, I am pretty happy with my setup but often I get stutters, lock ups whilst watching a file on XBMC that is on the cache drive or if the cache drive is working overtime and I am accessing something in the array.

I have the SAB, SickBeard, CouchPotato and HeadPhones all running on the cache drive and it seems to coincide with having all of these downloaders running.

My network consists  of -

1) 250GB Cache Drive SATA port

2) Dual core CPU and 4 gig ram

3) Gigabyte Ethernet on all connections throughout the house

I am considering the following options to help the lockups and hoping any one can provide some advice on which way to go -

1) SSD For cache drive, there is many arguments for and against this but would the increase of speed of an SSD help with running all these programs which are writing fairly constantly to the disk?

2) Moving CouchPotato and HeadPhones onto another box as these seem to be the most heavy users?

3) Simply putting a new SATA HDD in and hoping maybe the disk is just old and tired?

4) Don't if its possible but can you have two cache drives? Any maybe have one for programs and one for file storage? I read about V5 you can specify shares as "cache" only so not sure if you could use that functionality to possibly use a second disk for programs?

I am open to any suggestions, I am very happy with unraid but for me the cache drive having these programs on it seems to be struggling so looking for anyway to improve performance of the cache drive in particular?

Cheers!