What spec Mac would give a reasonable performance?

I really want to use Unreal, but it runs like a pig on my iMac, which is great for everything else (Photoshop, Unity, Blender, XCode…) but I am now forced to admit might be considered “old”.

It’s a "Mid 2011 with Radeon 6770 card and 12Gb RAM. I totally admit to being so eager to try Unreal Engine that I didn’t consider that Mac I bought 2 years ago would so totally fail to run it.

So there’s no way at all I can use Unreal Engine right now, and I’m dubious that any updates will fix that. Even a blank project sends my entire machine into a crawl. Not sure whether to cancel my sub and chalk it up to experience, or to let this drive me into buying more hardware.

So what is minimum spec Mac you suggest for running Unreal at a sensible frame rate? Mac Pros seem rather overpriced, and even iMacs get expensive if you up GFX card.

Which leads me to conclusion that even though Unreal now supports Mac, Mac doesn’t really support Unreal? And best option is to spend £1000 on a Gaming PC instead? Except that in all other respects I’d much rather be developing in OSX and not Windows. And especially as iOS development requires Mac anyway, so moving files from one machine to another every build is going to become annoying. (I suppose dual booting OSX on a PC and then running Unreal in OSX might be an option).