Just because Task Manager says the RAM isn't being used by a program in a direct way doesn't mean it's not still doing something. Sometimes that something is just waiting, having been allocated to a task that thinks it might in some way somehow sometime in the future. Or that something might be acting as insurance for people who don't think they need a swap file or something.
I recently took out half of my RAM because one of the 6 sticks didn't work very well (went from 12GB+no swap file to 6GB+swap file), and it feels like I went from a Lamborghini to a minivan my computer feels so sluggish. Of course, it's not sluggish by any means but it sure isn't as blazing fast as it was when I had 12GB and no swap. Maybe not all of that 12GB was ever close to used, but I would never have disabled the swap file if I only had 6GB. (A side note: an SDD + lots of ram + no swap file = no HDD noise = HEAVEN IN A CASE!)
It's so ironic that we, the very people who push the limits of this state-of-the-art technology, continue year after year after year to deny that more of something is better, when obviously it will be the norm the very next year, and probably is much better already!
2011: "8GB?? Overkill! Task Manager says I'm only using 2GB. 4GB is all you'll ever need!"
2006: "256MB of video memory is more than enough. Don't buy the 512 card."
2001: "40GB hard drive and 1GB of RAM? Overkill! You just wasted your money!"
1996: "Doom requires 4MB. If you think you need 16MB you're a fool."
1991: "CDs for computers? Crazy talk! If we need more space we'll just use two floppies! They're high density, you know!"
1985: "Why make DOS support more than 640KB of RAM? Crazy Talk!"
1981: "Floppy?"
The people who deny that more than 4GB of RAM is beneficial are the same people who say that humans can't see more than 24 or 30 FPS. Even if you say that I can't see over 30, I'm looking at my 120Hz monitor right now and I'm telling you it's way smoother than that 30 FPS game over there. Same situation here, but with memory instead of FPS. Trust your eyes and not the short-sighted people of the PC world (I'm probably one of them too, I am not pointing fingers at anybody in this thread!).
Yes, 8GB is better than 4. Excellent upgrade, OP!