The Turbo Boost clock speed is only around 15% lower than the other iMacs, though (2.7 GHz vs 3.2 GHz). It looks like the same processor as the MacBook Air. The bigger problem is probably memory--only 8GB, soldered to the board, and no option for more, even at time of purchase. Could be worse, though. With Mavericks, 8GB is about the minimum configuration for "normal people" tasks.

Mavericks works fine on my 2011 11" MBA with 4GB Ram. I don't use this machine for work, but it's still fine for everything else.

I'd believe that, but your MBA also has an SSD, which partially masks the effect of swapping out pages. True, SSD is an option for the new iMac, but it's not included in the base price.