Can't install more RAM, what will help?

Question

OK need a bit of help.
My elderly iMac has been a bit problematic lately, spinning beach balls, laggy, that chuggy noise which I always think is Spotlight indexing... (can't think of a more technical way to describe it!). I've just nosed around and saw a thread saying take a look in Activity Monitor at System Momory. This is what mine shows.
The thread I looked at kept saying 'are there a lot of pageouts, without actually defining what 'A lot' of page outs were! Nosed a bit more and think I may have too many page outs?
Now, thing is, I'm maxed out on RAM, in fact this machine should only take 4GB but I  managed to get it to accept 6MB, after doing some research and finding it was possible. So, I can't install any more RAM. Am also on Mountain Lion.
I have to trundle on with this Mac for a while longer. What can I do to improve my page outs and general speed of machine? Is it purely not having lots of applications open at once? I'm a designer so have CS6 installed, and use InDesign, Illust. and Photoshop. Is there anything I can do to get a bit more life out of this trusty warrior? Everything else on it works just fine.
I'm not 100% techie, but can usually sort out my  mac problems if someone explains clearly!
Spec of iMac: Alu 2.8GHz C2D 6GB SDRAM (should only take 4GB SDRAM but found out that it can take 6) 1TB HD

Answer 1

There is excessive swapping of data between physical memory and virtual memory. That can happen for two reasons:
You have a long-running process with a memory leak (i.e., a bug), or
You don't have enough memory installed for your usage pattern.
Tracking down a memory leak can be difficult, and it may come down to a process of elimination.
When you notice the swap activity, open the Activity Monitor application and select All Processes from the menu in the toolbar, if not already selected. Click the heading of the Real Mem column in the process table twice to sort the table with the highest value at the top. If you don't see that column, select
View ▹ Columns ▹ Real Memory
from the menu bar.
If one process (excluding "kernel_task") is using much more memory than all the others, that could be an indication of a leak. A better indication would be a process that continually grabs more and more real memory over time without ever releasing it. Here is an example of how it's done.
The process named "Safari Web Content" renders web pages for Safari and other applications. It uses a lot of memory and may leak if certain Safari extensions or third-party web plugins are installed. Consider it a prime suspect.
Another process often implicated in memory leaks is "inkjet8," which is a component of the HP printing softwre. If it's present, force-quit the process in Activity Monitor to solve the problem temporarily. If you don't use an HP printer, remove the software. Otherwise, if the problem is recurrent, update the software (which may not help) or contact HP support.
If you don't have an obvious memory leak, your options are to install more memory (if possible) or to run fewer programs simultaneously.
The next suggestion is only for users familiar with the shell. For a more precise, but potentially misleading, test, run the following command: 
sudo leaks -nocontext -nostacks process | grep total
where process is the name of a process you suspect of leaking memory. Almost every process will leak some memory; the question is how much, and especially how much the leak increases with time. I can’t be more specific. See the leaks(1) man page and the Apple developer documentation for details.