Not sure, though I really don't mind OSX, and with homebrew, it's pretty close to a 1:1 for most of my use on OSX...

The only thing that irks me a little is the muscle memory for using the option key for cut-copy-paste in the UI vs the actual ctrl key (ctrl-c etc) in a terminal...

You can easily remap it in System Preferences: http://support.apple.com/kb/PH13742

But, then I'm pressing command+c in the terminal window.

That's easy to fix. Use iTerm2, and tell it to remap modifier keys (to unflip them). If you use mission-control shortcuts (like move workspace), configure those keys in iTerm2 to "don't remap modifiers"

You want Karabiner https://pqrs.org/osx/karabiner/

Karabiner is amazing. I love that I can finally recommend it to people and they don't say "I have an iMac…"

@leephillips - good news is that linux installs fairly painlessly on the iMac 5K. I'm running Fedora 20 and it's going really well. Some slight funkiness with sound but I'm sorting that out now. Need hardware accel for gnome shell so required this workaround for the ATI drivers: https://bugzilla.redhat.com/show_bug.cgi?id=1054435

The custom hardware sits in front of an apparently stock standard AMD Radeon video card chip. I doubt it requires any software driver implementation.

VirtualBox is really good, and free.