Seconded, it's absolutely the CPU. This is a CPU that's nearly as old as the original Intel core lineup. DDR 3 and pcie 2. And worse performing generally. Spending $100 on someone's second-hand mid-2010 system. Paired with that graphics card should be wildly adequate. My main system runs a sixth generation i7 with an RX 580 overclocked. It isn't playing Doom the Dark Ages or most recent games maxed out, but it's no slouch.

I have a system of a marginally older vintage. A core 2 quad with 4 threads and a gtx 560. Also DDR 3 and pcie 2. It would be physically impossible for a system of those specs to even make use of most of an AMD 6700. The system bus alone would be bogged down, trying to even feed the GPU a fraction of what it can take. Not even counting other processing overhead.

PBR rendering is demanding on data rate. Way more than gourad shading or basic MIP mapped textures. Double the data or more.