Is there any way to use Safari 5.1's rendering engine for browser testing on OSX 10.8 (Mountain Lion)?
I found a project online which i think uses an old WEBKIT renderer..
http://michelf.ca/projects/multi-safari/ gives old versions, but i don't know which ones you will be able to run on your new machine. For myself,  I'm running 4.0.5 because of the reduced RAM usage.