One of my development machines is a Quad-core 5,1 (2010) so I think I know what you’re talking about. For this 2010 Pro I have a Sapphire 7950 Mac Edition which is demonstrably superior to the 5770 it came with - exact percentage is very dependent on the scene. I also have a stock PC EVGA Nvidia 680 GTX for comparison which provides a similarly big boost when used in the 2010 Pro. A GPU upgrade along those lines should help noticeably over the much slower 5770’s you are using now.
The biggest cause of stuttering in UE4 games (incl. ShooterGame & VehicleGame) is that UE4 defers submitting shaders to OpenGL until they are first used, which then causes pretty horrendous stalls in glCompileShader, glLinkProgram & the first glDraw* used. This is even worse on OS X because of the split responsibilities between Apple’s OpenGL.framework & the GPU vendors low-level driver extensions. This is far more noticeable on the 5,1 than my shiny new 6,1 (2013) because the newer CPU has vastly better single-thread performance.
Running UE4 under a VM/Virtualizer will not improve matters one iota - these programs provide 3D graphics support to the hosted Windows by piping D3D/GL commands through Apple’s OpenGL so you will face exactly the same performance problems you have now.
I’m working right now on trying to fix the terrible shader stuttering problems in UE4/OpenGL & the Github repo should already have the changes to switch to GL_ARB_separate_shader_objects in combination with a shader usage log so that program pipelines can be constructed at deserialisation, not first use. I’m still working on further improvements.