@sdoliva Thanks for reaching out!
Unfortunately, we will not be receiving any more 2020 Cannondale CAADX 105 bikes. Additionally, the 2021 CAADX 1 bikes are not expected to be back in stock until well into next year; likely late spring/early summer. Bear in mind that there are always variables in manufacturing, processing, and shipping (particularly at this time), so that timeline is subject to change.
Lastly, while the GRX group sets are specifically designed for performance on gravel, their categories do line up with Shimano's road group sets. The RX810 matches up with Ultegra, RX600 with 105, and RX400 with Tiagra. That being said, given gear ratios and design considerations in each group set, it is very important to take into account what kind of riding you will be doing. Primarily road riding with lots of flat stretches? 105 is probably your best bet. Looking to leave the road behind and climb some hills? RX400 will likely meet your needs better. Ultimately, the best decision for you is going to be the group set that matches your style and riding goals closest.
Hopefully this helps, thanks!