After recently discovering promising details on FocusPulling.com regarding Premiere's April 2018 update, I decided to spend an afternoon crunching out exports to see if performance could be effectively doubled by enabling internal graphics via processor so that, essentially, a second GPU would work alongside an external graphics card. This is what I found.
My editing computer can be found at this PC Partpicker list. I'm OCing the CPU to 4.5Ghz.
Utilizing a simple interview file shot on a Sony FS5 in XAVC 8bit 4:2:0 (3840x2160), I exported the same 60 second clip with different settings in Premiere as well as the system changes outlined above.
There was some discussion in the comments on the the FocusPulling article regarding the efficacy VBR 1 Pass vs. VBR 2 Pass. This is relevant because the Dual GPU setup does not allow VBR 2 Pass for... some reason. In addition to simply timing the exports, I included samples of VBR 2 Pass exports to compare for quality.
My assessment is below the image. You should be able to open the image in a new browser tab to magnify to 100%. Image dimensions are 3334x5093. Frame reference numbers are on the subject's left shoulder. Grades were done using Lumetri. Single GPU exports utilized Software Encoding. Dual GPU exports utilized Hardware Encoding.
It's pretty clear to me that frames 2 and 5 are the clearest. This is evident on the subject's forehead and pupils, especially when compared to frames 3 and 6 where the compression is downright messy. Interestingly, the midtones in frames 3 and 6 seem to have brightened up a bit - I'm not sure if compression is responsible for that or something else entirely.
My conclusion is that running a Dual GPU export wherein the second GPU is the processor simply cannot replace the VBR 2 Pass export option. The speed increase on this scale also isn't worth the switch. Of course, each project differs and some may be perfect candidates for this type of setup; case in point, in 2017, I filmed a weekend conference and delivered 3 sets of 14 DVDs to the client.
If you have any questions or insight, please feel free to contact me at email@example.com