The realistic minimum amount of RAM for Photoshop these days is 8 GB. The Adobe-stated minimum requirements are way too optimistic.
I run Photoshop CS6v. 13.0.6 (Mac) with 16 GB; others have 32 GB, 64 GB and even 128 GB of RAM.
You also want plenty of hard drive space, and ideally a dedicated, physically separate hard drive just for Photoshop scratch.
The rule of thumb I follow to figure out scratch space says to figure on 50 to 100 times the size of your largest file ever multiplied by the number of files you have open. I have seen the scratch file exceed 800 GB once, an admittedly rare occurrence, but it often exceeds 200 GB when stitching large panoramas and the like.
As an example—and stressing that I'm aware that others have even more scratch space than I do—I keep two dedicated, physically separate hard drives as my primary and secondary Photoshop scratch disks and a lot of GB free on my boot drive for the OS. I also have 16 GB of RAM installed.
Additionally, if you only have a single HD, i.e. your boot drive, you'd need it to be large enough to accommodate both the swap files of the OS as well as Photoshop's scratch.
I didn't even know they did 6 gigs. Is that using the expansion slot? If not, I'd add in as much as you can.
I have a Vaio i5-2410 @ 2.3GHz with 8 gB ram (I got the 4 gB and then put in another 4 myself). It gets bogged down with intensive operations on large files, and I only do 16 bit, I'm sure 32 is going to give it trouble. But I've done plenty of work compositing multiple RAW images from a 20 mP camera with dozens of adjustment layers. But I'm also usually just about maxed out of Ram, with Photoshop, Lightroom, and DxO. I've also had plenty of crashes. So much so I ended up building a PC, but that's another story.
A couple issues I've had with my Vaio:
The AMD GPU doesn't play nice with PS. That's what crashes it. Sometimes it's worse than others, but it definitely "flares up" at times and even the simplest of operations will crash it. I've tried all kinds of updates, and rolling back drivers and whatnot. None of it works. Turning off graphics acceleration might of helped, or it might have been placebo. My main solution is to save often and completely close and reopen PS in-between major projects.
There absolutely is an issue where PS doesn't clear out the ram when I close a big document (I frequently work on projects in the 2 - 3 gB range). I also did a lot of research on that, and many swear that it's how it's supposed to function, but mine gets so bogged down it can't even open a small photo. It doesn't do it consistently, but when it does it's obvious that something is wrong. My solution is to simply close and reopen PS.
All Windows computers, in my experience, slow down after a few years. Task and registry cleaners only work so much (and are supposed to be unnecessary in Windows 7). People attribute it to the computer being old, but if you simply (ok not simply) wipe your drive and reinstall Windows and your programs it suddenly works like new again. I had to do this to my Vaio a month ago after my hard drive crashed. I also upgraded to an SSD. It was a pain in the ***, and took a whole night of loading programs and tweaking things back to how I had it, but it runs better than it ever has. Knock on wood - Photoshop has been running a lot better too.