Here's the display performance comparison between Rhino 5 64-bit and the current Rhino WIP. To make the test results comparable, all tests have been done on the same machine.
CPU: Intel Core i7-6700K @4.0 GHz
Display Cards/Chips: Nvidia GeForce GTX 770, Nvidia GeForce GTX 970, Nvidia Quadro K620 and Intel HD 530
System: Windows 10 64-bit
Test model: FireEscapes_Caustic_Test.3dm (152MB with render meshes. It's modified from one of @BrianJ's models, thanks.)
Information reported by the PolygonCount command in both Rhino 5 and RhinoWIP:
There are 265768 quadrilateral polygons and 186908 triangular polygons in this model.
There would be 718444 total triangular polygons in this model after forced triangulation.
(The model was not re-meshed in Rhino WIP.)
Test: Use the TestMaxSpeed command with default options. Test three times in every display mode and use the average.
High-end GeForce cards have similar performance with the low-end Quadro card in Rhino. The price of a Quadro K620 is about a half of a GTX 770 or 970. (I don't have a middle-level or high-end Quadro to test.)
Upgrading from GTX 770 to 970 does not make sense if it's only used for Rhino.
Intel HD 530 may compete with middle-level GeForce cards. (Just a guess. I don't have a middle-level GeForce to test.)
Intel HD 530 has greater improvement on Technical, Artistic and Pen display modes in Rhino WIP.
Intel HD 530 is 4x faster with hardware acceleration turned on than turned off. It can be hardware accelerated.
I didn't see obvious display problems with Intel HD 530 in the test. I'll try to mainly use Intel HD 530.
(I'm not promoting Intel HD series by the way.)