So I went ahead and upgraded my CPU and Mobo to a i7-7700 Kabylake with the appropriate motherboard BIOS update. Wanted to share the benchmarks for people who want a general idea of what to expect. Same video card (GTX 1070) and same SSD (Samsung 850 EVO) on both. Same maximum setting but on borderless as FFXIV becomes unresponsive on my rig at fullscreen DX11 for some reason.
i5-4670 Haswell Benchmark:
i7-7700 Kabylake Benchmark:
This accounts for an overall 1000 score increase. The following observations were also made on the data not present on the general screen.
1. Overall increase in average FPS from 88fps to 96fps. Net 7fps gain all things being equal.
2. Almost no screen tearing, as the benchmark has no Vsync.
3. Overall reduction of loading times from 22s to 18s. Across all 6 scenes it's anywhere from 0.4s to a whole second.
My observations:
1. FPS performance gains are less than 10%, so overall the improvements from a CPU upgrade are negligible at best. From this POV a video card upgrade will be more cost effective.
2. I assume that the decreased screen tearing is due to a better performance match up between CPU and GPU. This could be a good thing for those wanting to really do a CPU upgrade, because maybe now we can turn off Vsync and expect better performance gains.
3. Since my mobo was the same and the adaptors are the same, we could account the loading time improvement squarely on the CPU and not on my SSD. 1 second loading speed reduction might be generally negligible unless you're in highly populated area.
Conclusion: Get a better video card even if it's more expensive. Despite MMO's being CPU heavy, FFXIV will run better on a comparative GPU upgrade than a CPU one. Any 4th gen Intel processor and presumably AMD equivalent will be more than suffice. I can't recommend a CPU upgrade alone for those wanting improved performance.