You will also notice that the article mentioned that the Windows* drivers support the NBASE-T technology, but only in Autosense.

Provides 2.5 GbE and 5.0 GbE link speeds over CAT5e/CAT6 cabling deployments. Firmware upgradable to IEEE 802.3bz(1) One exception appears to be the Qnap 10GbE PCIe Card QXG-10G2T-107 which is a dual port but has a fan for cooling. NO WARRANTY. The Materials are provided “as is,” without any express or implied warranty of any kind including warranties of merchantability, non-infringement, title, or fitness for a particular purpose. The Materials may include pre-release software or algorithms and may not be fully functional. Intel is not required to maintain, update, or support the Materials. If a configuration setting is not displayed, it's not available for your device or for your Windows* version. Termination. Either party may terminate this Agreement, with 30 days written notice, at any time for any reason. This Agreement will automatically terminate upon (a) Your breach of the Agreement, (b) an allegation that you do not have authority to bind your employer to these terms, or (c) Your assertion that an Intel Component, the Materials, or any product based on any Intel Components or the Materials infringes Your patents.and work properly (with slower speed). Since Intel 82599ES 10 Gigabit lan card is compatible for Qnap NAS system up to now (maybe they will cut the support after seeing this post). On: Driver does wait for Auto Negotiation. If the speed is not set to Auto Negotiation, the driver waits for a short time for link to complete and then reports the link state. I have linked and quoted the official Intel advertisements and documents above multiple times, that clearly promise in writing, that Intel would be upgrading from draft NBaseT to official standard IEEE 802.3bz support, post-launch of X550, as a free firmware upgrade.

For additional information on Microsoft Hyper-V virtual NICs on teams and VLANs, refer to the Microsoft* Windows* Driver and Software Installation and Configuration section in the Adapter User Guide for Intel® Ethernet Adapters. Enable Jumbo frames only if devices across the network support them and are configured to use the same frame size. When setting up Jumbo Frames on other network devices, be aware that different network devices calculate Jumbo Frame sizes differently. Some devices include the header information in the frame size while others do not. Intel®adapters do not include header information in the frame size.To answer your question, technically only the TrueNAS server will be able to use the 10Gb. Although, if multiple machines are trying to access it at the same time you will notice a difference using 10Gb over 1Gb since your drives can more than likely go faster than 1Gb speed. Just to avoid your confusion on my question - I have switched from Windows, and I am now using Linux (because Drivers and OS do not matter to this request!).