I replaced my Mac and PC years ago with an iMac and haven't looked back but I use a console for gaming, not my computer. Over the years there have been some complaints from hardcore PC gamers involving graphic driver issues. I don't pay much attention to them since they don't affect me or the people I know. So I'd suggest that you look more closely in the iMac forum for recent complaints (if any) from PC gamers.
Since you are looking at pretty similar cost and since
space is a consideration, the iMac, I believe, is pretty
much the obvious choice.
One thing you might have overlooked, is that for gaming
intensive tasks with Windows games is concerned, natively
booting via Bootcamp is the obvious choice. However, with an
app like Parallels Desktop or VMware Fusion, you can also
use that Bootcamp partition within a virtual machine environment
on OSX. This would mean with nearly all other apps you can
run Windows within the virtual machine will still running OSX
thereby not needing to reboot.
More than likely most of your ither PC apps will likely work
quite well within a virtual machine. For instance, I use things
like MATLAB, ORCAD, and other engineering type of applications
within a virtual machine environment, including a Link Instruments
500 MHz USB based oscilloscope.