I do most of my development on a 2013 rMBP 13" hooked up to an external display, which suffice to say isn't the fastest machine but most of the time gets the job done fine.

Xcode autocomplete is just miserable though in autocompleting Swift, as in most of the time I can type out what I want faster instead of waiting for Xcode to catch up. Or worse, it will try to autocomplete and not be able to keep up with my typing due to it lagging. My CPU is consistently fully pegged just typing, not even during compilation phases.

I honestly find myself coding a bit in Sublime Text 3 and pasting into Xcode when it's particularly terrible.

On more recent Macs (if you'd call them that, ha), such as a recent 5k iMac, does Swift autocomplete in Xcode quickly for you? Or is Xcode sluggish regardless of the machine? Hoping to pick up a newer iMac whenever the new ones come out and I'm curious.