Frequent frame drop/bad performance after removing bad RAM

Operating System ==================

Windows 10

Computer Specs (PSU, GPU, CPU, RAM, Motherboard) ==================

PSU: Corsair CS750 750w

GPU: Asus Strix GTX960 2gb

CPU: AMD Phenom II X6 1100T Processor, 3300Mhz, 6 Cores

RAM: Corsair XMS3 DDR3 sticks. Originally 2x 1600mhz 4gb, 2x 1333mhz 4gb (16gb total). Now 2x 1333mhz 4gb (8gb total)

Motherboard: Asus m5a78l-m/usb3

Speccy Link ==================

N/A

Description of problem ==================

I noticed slightly worse performance than usual on my PC, thought nothing of it (put it down to a program updating or something) but when I started CSGO I was getting only about 30fps, normally I play at about 150fps. After looking in my task manager and seeing I only had 4gb of RAM being recognised I put it down to bad RAM. I tested each stick using windows memory test, and one out of the 4 was faulty. I have removed this and my PC performance still seems OK in general tasks but when gaming I still getting problems making it unusable for gaming.

For example when playing CSGO I sit at about 90fps (already a big drop considering its only RAM I've removed) but every couple of seconds it drops to 30fps, then back up to 90fps again. It is related to the action on screen but will do it even if I just stare at a wall too. I have tried with Overwatch too, which also has the same problems, albeit more consistently low frames.

When this issue began ==================

2 or 3 days ago after finding bad RAM

Recurring issue ==================

Yes

Date of purchase ==================

N/A

Under Warranty ==================

No

Cause/Steps to recreate the issue ==================

Removing 1 stick of RAM, or 2 sticks of RAM, from a normally functioning PC.

What I've tried so far to resolve the issue ==================

Tested all my RAM sticks and found the one faulty stick, and removed this.

I tried first to run with 12gb of RAM (3 sticks) but read this may be my MOBO switching to single channel, so I took another stick out and tried with 8gb of RAM. Still the exact same problem.

I have cleaned out the case for any dust, however it wasn't that dusty. I did look at the CPU and there wasn't much heat paste left, I will get some of this today but the CPU still seems to be cool enough anyway. Haven't noticed it being very hot.

I have tried reducing all my graphics settings to very low - I still get the exact same problem, just with slightly more frames dropping to the same level every few seconds.