Hey @zilma-zaz,
Just foloowing up on this. Did a couple of tests there on two identicle machies with RADEON VIIs and i9-9900Ks.
Running SysDef- 19,1 (iGPU)
Running SysDef- Imac Pro 1,1 (No iGPU)
You are correct. iGPU does indeed slow things down. Not sure why i was getting hung up on it...