Is there a reason you are not moving to CS6? Not saying its a huge improvement, but if your paying for an upgrade why not get the latest? CS6 is noticeably snappier, at least compared to CS5.
If you are neutral in situations of injustice, you have chosen the side of the oppressor. If an elephant has its foot on the tail of a mouse and you say that you are neutral, the mouse will not appreciate your neutrality. Bishop Desmond Tutu
I'm on an 8 core with 4 gigs of RAM, and 10.5.8, and I really didn't want to worry about upgrading the system software as well. From what I understand, 6.0 needs Snow Leopard at a minimum, and I'd probably want to double the RAM and upgrade to Mountain Lion.
MacBook Pro 2.2 15"
G5 2.0 DP Desktop
Slowly collecting all the colours of the iMac...
Adobe was my first call. They refused to sell anything other than the current version. (I'm not a volume licenser)
There's no reason to not become a volume licensor, nor any minimum purchase to become one. You'll have to phone the volume licensing sales department to get an older version, but it can definitely be done.