I just went through the same process. Had 27" iMac that was about 4 years old and priced the latest version at $2900 with just a couple of add ons. Used Cyber Monday as my excuse to go through with it. I built one with the Haswell 4770 3.5 (running at 3.84), 3GB GeForce 780, 32GB ram, 27" SRGB ASUS monitor (@ 2560x1440), 128GB SSD for boot/operating, 1TB SATA for job files (and of course power supply, motherboard, case, etc) for $2100. I'm using the tonymac setup for dual booting into 10.9 & windows 7.
So far so good. Only thing that I find doesn't work is the Preview app in 10.9. NBD on that one.