I am only a newbie who is anxiously waiting on the iMac update but my market research would show that Apple have always been at the front when it comes to spec. The current iMac is almost 500 days old and believe it or not the competition are now only starting to offer iMac equivelants or close. sure you can buy PC's at half the price but at half the spec ( forget about custom builds) or the PC's with similar spec is only approx £150 cheaper if that, throw in Nvidia GT??? and your there.
My guess is
sandy-ivy, 8GB RAM min, Nvidia Graphics(as per MBP), HD 1080p + screen, 128 GB SSD + 1TB hd
if the update doesnt come close to this then i will seriously consider buying the current model , but obviously at a lower price