So I have a base 21.5" iMac i5 2.5GHz, 500gb (5400) with 8GBs of ram. I have been messing with Lightroom a lot recently and thinking of bumping to 20GBs for my photo and video editing. But, was offered $725 for my iMac tonight and am thinking that maybe I should get a new one. My question, how big of a jump would i see between my model now and the 21.5' with 8GBs of ram with a 2.7 fourth generation. Also see that in the refurbished store, they have a 27' with a 3.2 i5 and 1TB 7200 hard drive for $1399.