Having read all of the above posts I'd say you have a pretty good pile of advice to go on. I'll explain in simple terms (from my Uni experience) some of the possible pro's and cons of adding more memory, and also the circumstances it maaay be of use.
The first point I'm going to put to the forum is that having more individual RAM sticks installed can sometimes on its own lead to faster data transfers to-from the computer. For example one 4Gb card would probably give slower performance than two 2Gb cards. This is because the memory can be accessed almost in paralell from two sticks. Now this ONLY works if the system architecture is designed to allow it to happen, and I have NO CLUE if it is on iMacs or not.... So if anyone can do a test with one 4Gb card then swap out for two 2Gb cards it'd be greatly appreciated - even if it proves me wrong.
The second factor that will make a difference to you only comes into play IF you keep your computer on standby for a long time - i.e more than a few days at a time.
When you boot up your Mac (having previously been turned off) and open a program, that programs code is copied to the RAM from the HDD to be used by the processor. When you CLOSE the program though, a lot of the code needed to run the program will remain in the RAM so that the program will open faster should you decide to use it again. Test this by timing a program immediately after a reboot. Close it right away and time it opening again, the second one will be shorter.
Now, IF you use a lot of programs over a two or three day period, but not all at the same time, your RAM will gradually rill up with the base code for these programs so that they will open faster the next time you use them. However from using my iMac like this the amount of RAM that gets tied up never gets above (for my uses) about 3Gb including any currently running programs.
I have 8Gb installed on my iMac and have never went above 40% and thats with EyeTV using a 1 hour TV buffer on RAM, Handbrake, Photoshop, iPhoto and maybe iTunes open too, as well as 3 days worth of previously opened stuff.
Conclusion to all that: 4 RAM sticks MAY give you slightly faster speeds than two. Unless you use massive amounts at a time, or lots over many days without reboots in the middle you wont notice an increase just now. Prices will only go down for RAM so unless you NEED it you will save money waiting till it gets cheaper.
The first point I'm going to put to the forum is that having more individual RAM sticks installed can sometimes on its own lead to faster data transfers to-from the computer. For example one 4Gb card would probably give slower performance than two 2Gb cards. This is because the memory can be accessed almost in paralell from two sticks. Now this ONLY works if the system architecture is designed to allow it to happen, and I have NO CLUE if it is on iMacs or not.... So if anyone can do a test with one 4Gb card then swap out for two 2Gb cards it'd be greatly appreciated - even if it proves me wrong.
The second factor that will make a difference to you only comes into play IF you keep your computer on standby for a long time - i.e more than a few days at a time.
When you boot up your Mac (having previously been turned off) and open a program, that programs code is copied to the RAM from the HDD to be used by the processor. When you CLOSE the program though, a lot of the code needed to run the program will remain in the RAM so that the program will open faster should you decide to use it again. Test this by timing a program immediately after a reboot. Close it right away and time it opening again, the second one will be shorter.
Now, IF you use a lot of programs over a two or three day period, but not all at the same time, your RAM will gradually rill up with the base code for these programs so that they will open faster the next time you use them. However from using my iMac like this the amount of RAM that gets tied up never gets above (for my uses) about 3Gb including any currently running programs.
I have 8Gb installed on my iMac and have never went above 40% and thats with EyeTV using a 1 hour TV buffer on RAM, Handbrake, Photoshop, iPhoto and maybe iTunes open too, as well as 3 days worth of previously opened stuff.
Conclusion to all that: 4 RAM sticks MAY give you slightly faster speeds than two. Unless you use massive amounts at a time, or lots over many days without reboots in the middle you wont notice an increase just now. Prices will only go down for RAM so unless you NEED it you will save money waiting till it gets cheaper.
, but it may be useful if you run lots of memory hungry applications, I use illustrator and photoshop on daily basis together, and I've only got 4GB Memory, along with that I have lots of safari windows and itunes open.. I would consider getting the memory if your running a lot of adobe apps together or lots of memory hungry applications..