Its just the Kernel module, not the driver that is Open Source. It's still using the Proprietary driver, so a parity in performance is expected. I think people getting overly excited about this don't understand its still the same video driver.
Don't get me wrong, I'm a longtime Linux user and for the longest time was using a Nvidia card too. And I do understand the excitement that Nvidia taps more into Open Source. But this is an almost negligible step in my opinion and doesn't matter much in real world. Yeah you can booh me for that, but unless the video drivers themselves get opened sourced with a compatible license, I can't get much excited for. What do you think?