i can tell you this right now. I dont have an SSD. I have a mech drive and my mech drive is pissing me off. I am in the same boat as you OP. I do know you wont gain any FPS gain but will gain way faster texture loading. my current HDD loads like a moron even at times makes my firefox freeze cause my HDD isnt keeping up to the multi tasking. My game textures to a point i do notice load slow.
My HDD is my biggest lack in my PC at this moment. Wish I could of hit the M4 when it was $130.00 but now im stick paying 148.00 cause I am tired of this stupid mech drive.