Where did you get that 8% number from? If it's from a bottleneck calculator, then ignore it, because it's terrible advice. Bottleneck calculator sites are worse than useless.
@fefolavelaz - whether or not the upgrade in GPU will be beneficial requires knowing a few things:
- What is your monitor's resolution?
- What is your monitor's refresh rate?
- Does your monitor have FreeSync, GSync, or neither?
- If FreeSync, what is the FreeSync range?
- What games are you playing?
To use an extreme example - assuming a target of 60Hz/60fps, if you're playing a first person shooter, and running 1280x720p resolution, then there's no point in upgrading the GPU. But if you're running, say, more than 1920x1080p, then there's a benefit to upgrading.
EDIT: and I concur with
@logainofhades , replace that PSU with a higher quality one.