I want to buy RTX 30s for asus Motherboard p9x79 pro.
1. Does they compatible?
2. What is your additional advice?
3. If yes, which RTX 30 brand manufacturer is worth buying by price and efficiency?
Be aware that your platform is more than 10 yrs old with PCIe3 standard where as the card is PCIe4. There will not only be performance limitation but also bandwidth limitation. Although rest of your hardware looks good quality, it is still old school. Theoretically it is supposed to work, but you might run into compatibility issues with drivers and updates.
If you can upgrade to a recent platform it will be more easier and convenient for you.