Hey,
I just added the Samsung 950 Pro and the specs for that above.
I can't judge if it is worth it or not but it will help a bit any time you heavily access the SSD such as bootup.
*You still have not explained your problem. You say "speeds aren't consistent at all" but I don't know what you mean by that.
If it's about GAMING and your FPS, then the SSD has nothing at all to do with that, the drive is only used when a game or later loads are happening; otherwise the CPU is reading from your DDR4 memory. Fluctuations in frame rate are normal, so please be SPECIFIC as to the problem.