I would go with the suggested ram settings in the memory slider. Going over can affect other programs other than the finder and in my experience, I have never seen much of a benefit.
You have 32 GB so you can give it a try and if you run Mt. Lion,look at the Activity Monitor and see how it affects the memory allocated to the system. Look at your Page outs to Page ins. Page outs should be 20% or less of Page ins. Some prefer 5%. The less the faster your machine will perform.
The percentage shown is the maximum percent of currently available RAM at a given moment that Photoshop can use after the OS and all other running application and processes have grabbed whatever they need to run. It's a constantly, dynamically changing amount of RAM.
With 32 GB of RAM you could conceivably set it to 100%. It's not 100% of the total 32 GB of RAM installed, but, as explained above, a percentage of whatever currently available RAM at a given moment that Photoshop can use after the OS and all other running application and processes have grabbed whatever they need to run.
Set it to leave 1 to 1.5 GB of free RAM. That's sufficient for most systems.
If you want to use Photoshop simultaneously with another RAM hog of an app, you may need to change this approach.