The most relevant fact we noticed is that your motherboard is not certified to boot from the Intel® SSD 750 Series, so we cannot guarantee that it will operate according to specifications. You might want to check back with the motherboard manufacturer, they may be able to provide additional recommendations and configuration to improve the functionality of your PC.
For reference, you can review the document Intel® High Performance Solid-State Drives — Booting an NVMe* PCI Express* Solid State Drive, it contains some examples of BIOS configurations and requirements (Note: Intel® X79 Chipset motherboards were not tested/certified to operate with NVMe drives). Furthermore, if you have been informed by the Asus that they are working on a new BIOS, it may be good to wait and check if this helps with this situation as well.
In addition to this, please make sure you are using the Intel® Solid-State Drive Data Center Family for PCIe Drivers.
The advertised performance of this drive is found in page 8 of the Intel® SSD 750 Series Product Specifications. We cannot refer to the values you obtained in your test, since the test configuration are not the ones recommended to take advantage of the 750 features. We recommend using IOMeter* and modify the parameters depending on the type of test you are performing. For more information about this, you can review the document: Intel® SSD 750 Series — Performance Evaluation Guide