Right now the external GPU market is a bit of a mess, full of hacks, incompatibilities, half-adhered-to standards, and artificial limitations from the likes of Apple. The folks over at eGPU.io are putting in some solid work to make sense of it all (as spotted by AppleInsider), and they've just had a surprisingly great result with the latest Nvidia drivers, a GTX 1080 Ti, and a 2016 15-inch MacBook Pro.
This is, of course, courtesy of the new Mac drivers that Nvidia just released, which bring the Pascal 10XX series of cards to macOS for the first time. Of course, you can't actually put a 1080 Ti inside a modern Mac, unless you're building a hackintosh, so an external GPU enclosure is your best chance of accessing this power from within macOS.
In tests, running inside an AkiTiO Node or Mantiz Venus enclosure, eGPU.io found the 1080 Ti put in benchmark scores ranging from double to four times the speed of a MacBook Pro relying on stock internal Radeon Pro 460 graphics. Speeds were boosted further when the external GPU was used with an external display, instead of routing the video signal back into the MacBook.
Apple's recent 15-inch MacBook Pro has an advantage over many laptops with Thunderbolt 3, because the connector is basically hooked up directly to the CPU, instead of being routed through the PCH (which handles a bunch of other I/O like networking, storage, and other USB ports).
Really, the new Nvidia driver support is just gravy on top, because the 1080 Ti didn't outstrip the last-generation 980 Ti by much in tests — which points to remaining bottlenecks in the setup.
An external GPU is still an expensive way to improve your workflow: a quality enclosure is around $500, and then a card like the 1080 Ti goes for around $700. Also, macOS support for external GPUs is improving, but it's still not plug-and-play. You might be better off doing your work on a Windows desktop, or trying your luck with with a hackintosh, but if a souped-up MacBook Pro is truly what you need, it does seem like the age of the eGPU has arrived.