Well, wait untill the refresh, it's next Tuesday and you'll know
What are you planning to do with your iMac? The current iMac is powerfull enough for most tasks. Choose that one as refurb when the new iMac comes out. However if you are planning to play newer games, do (HD) video-editing or other demanding tasks you'd better pick the 2011 iMac.
The new 2011 iMac will have faster Sandy Bridge CPU's and Thunderbolt. Probably also better GPU's.
But I also want to add you'd better look around here on Macrumors before starting yet another topic. This has been discussed for multiple times already.