If you have USD $2,500 to spend in a new piece of hardware, you can get the new iMac with a 27-inch Retina 5K display. This 5K (what is 4K?) has more pixels than even because with its resolution of 5120×2880, it has 67% more pixels than a 4K display.
This new iMac comes with a 3.5 GHz quad-core Intel Core i5 processor with Turbo Boost speeds up to 3.9 GHz, and for the first time can be configured with a 4 GHz quad-core Intel Core i7 processor with Turbo Boost speeds up to 4.4 GHz.
The graphics side is powered by an AMD Radeon R9 M290X (with the possibility to get also a Radeon R9 M295X).
OS X 10.10 Yosemite as well as a 1TB Fusion drive are also in the party.
Complete press release can be found here: Apple Introduces 27-inch iMac with Retina 5K Display