I had similar issues to everyone else with "shadow acne" popping up. The thumbnail for this project shows it very slightly, but here are a few of my challenges in progress before getting the bias correctly tuned.
113ms render time on 8 threads for the cornell-ish box-ish scene.
MacBook Pro (15-inch, 2016)
2.7 GHz quad-core Intel Core i7 Skylake (6820HQ)
16 GB 2133 MHz LPDDR3 RAM