I basically agree with the above.
*Don't waste money on a fast SSD. Benchmarks aside, the real-world advantage of a drive faster than say, a 2.5" Samsung 850 EVO are likely not noticeable.
Perhaps specific video EDITING scenarios might benefit but other than that I can't think of much.
Keep in mind Windows will BUFFER into main system memory (i.e. DDR3) programs and data you use. for example, if I open MS WORD once it will open from my SSD the first time but the second time (unless I reboot) it opens from my DDR3 memory. Windows 10 may even pre-buffer data after I reboot but I don't know the details.
You can probably shave a few seconds off boot time with a really fast PCIe SSD but it's really hard for me to justify the added cost. I suspect most desktop users buying PCIe SSD's are largely wasting their money.
Other:
You should read your motherboard manual if interested. GPU loss of performance is not an issue, however you may deactivate or lose performance on some PCIe slots, M.2 or SATA connectors depending on what PCIe slots are used.