I have 3 ssd's... one for the main OS including PS, lightroom, etc. I have another small one for a scratch disk for PS and another one for the OS virtual memory. I have 8 gig of ram and using a scratch disk on separate SSD drive really helped the speed. in your case if you don't run PS you can use the SSD for the temp files, etc for lightroom. not sure if lightroom 4 supports scratch disk or not.
BTW with PS and OS on my ssd drive PS boots in less then 5 seconds
I would get the high end ones (I have ocz vertex 3 and agility 3) as the older ones (even a year old) are only 1/2 as fast)
my system is just an out of the box HP that supports ddr2 8 gig. I upgraded the power supply and video card ((g-force 550 si) as I run dual monitors as well.
It is also around 4 years old.. intel dual core first or second version conroe core.. still does a good job but I did spend a few bucks to upgrade as you can tell
now that I read back to your post yours is faster then mine
good luck