What resolution are you running at? I'm on a 1080, 6700k @ stock with every setting maxed at 1920x1200 and getting 90-110 fps just driving around surfers paradise (so far just day time free roaming). Feels much smoother now and so far no noticeable stutter.
2560x1440, the game is probably still reasonably CPU bottlenecked so we're not getting the most out of either of our GPUs at these resolutions, but the bottlenecks have been seemingly significantly reduced.