Okay! I've been able to isolate the problem. After trying everything high and low, I went for the SLI bridge. Lo and behold, there is the problem! Like stated in other forums as well, the SLI bridge connection is responsible for the flickering. My bridge currently isn't embedded all the way but the flickering is gone for good.
I believe the problem lies in my SLI bridge being of low quality. It came included with my Asus mobo. I'll swap it out as soon as possible.
Thank you a lot mousemonkey for helping me rule out the possibility of it being a PSU issue.