Professional Photographer - Buying a 27" iMac

[emmamac]

Hello everyone,
Im currently in the market of buying an imac 27 and im a professional photographer ive always used windows and now have purchased a new DSLR that is 36mp the problem i have is when working in photoshop cs6 it is struggling with file size so this the main reason for purchase of my new imac 27.

My questions,
i know there is a new imac 27 on its way to us ive been to currys today who tell me i can have the latest model on a i5 for almost £1600
but there is a friend who is selling his imac 27 (Mid 2011) 3.4 GHz, Intel Core i7,1TB Hard Drive/ 4GB RAM, Quad Core and comes with 2 years apple care.

Now what would you guys go for a new imac or the second hand one he wants £1500 ?????????????????????? HELP