Currently looking at iMacs in ebay. I have narrowed it down to 2 iMacs: one of which has 12GB of RAM (no apple warranty, only seller warranty for 30days). The other has 4GB of RAM and AppleCare until June of next year. I won't do video/photo editing or gaming, so I guess the iMac with the AppleCare is the way to go? Would 12GB of RAM provide a huge improvement when performing not too demanding tasks?