iMac slow and unresponsive after Mavericks There have been a few questions and answers about memory usage, whether one should pay attention to the Activity Monitor, that Memory Pressure is more indicative of a system being maxed out on RAM, etc.

Ever since Mavericks was installed, copying and pasting from Safari to Excel freezes the computer for a few minutes. I'm watching now as Memory Pressure increases after copying the data from Safari. If I try and paste the data into Excel, Excel won't take it. After several minutes and a very sluggish iMac, memory is freed up (subtracting memory used from Physical memory) and I can paste the data without a problem.

It looks as though the iMac is trying to shuffle memory around (the compression, I believe?) and until it shuffles it I can't do anything with the data I copied.

The iMac only has 4gb RAM, as the geniuses said that was more than enough. It always has been until Mavericks.

iMac is 27-inch, Mid 2011.

I was going to purchase more memory until coming across posts detailing sluggishness after installing Mavericks.

Now I'm not sure if the problem lies with Mavericks or memory. If I installed 16GB, would the same thing happen? Would the OS still use as much RAM as possible and need to "shuffle" memory around in order to free enough up to finish my copy and paste?
My recommendation would be install mavericks again. I upgraded both my Mac's and had problems with sluggish performance and app's not responding.