In Hong Kong the price of the top-end i7 27in iMac should drop by at least US$250 once the 'new iMac' is released if past prices of refurbished machines are a guide, basically, it should set you back HK$12,980 - the price of the current low-end entry model 27in - this in my opinion will be an excellent price for a used i7 27in iMac - obviously, Apple's prices in Hong Kong are among the cheapest in the World as there is no sales tax in the Territory.
I cannot vouch for USA, Canada or UK, but usually, I purchase all my Apple products in Hong Kong and take a few items back to the UK for friends and family - my next trip next month will see me drop off a 2010 iMac 21.5in 3.2Ghz i3 with AppleCare for 18 months - Apple even have to swap out the HDD on it and I'll push for a replaced LCD panel as well - not bad for £500, or half its original purchase cost in April 2011.
Hope this helps, but if Apple does update the iMac line by months end, I think it daft not to get a refurbished 27in model which may be either brand new, or have a few unexpected updates like a 2T HDD, 2G VRAM and 8G RAM.
Hope this helps.