I suggest you use you SSD as boot drive and keep your cache on RAM disk. Ram disk add some time to you boot time but it's worth it because of reduced writes on the SSD and there wont be a big speed difference whether the cache is on SSD or RAM Disk. RAM Disk are a little slower but save your SSD from a lot of writes.
EDIT: i just started RAMDisk. my total RAM is 2 GB but for some reason the max limit was one GB, so i set it for 512 MB now my browser cache and system variables (temp,tmp) are running at blazing speed, strangely, even my 5400 RPM is experiencing quite a speed boost. I strongly advise using RAMDisk for cache, sometimes RAMDisk is faster than SSD and even if not, it saves you a most of the writes if you choose it for both...