Which?
Which?
This question really puts me off... I wouldn’t pay that much for a board. I’m sorry if I came across as dismissive.
The B550M Aorus Pro (matx) and the B550 Gaming X (atx) offer similar power delivery capabilities, making them interchangeable. You might also consider the Asrock B550 Phantom Gaming 4/ac (ATX). All these options are reliable choices; you won't face any issues. Your case supports both ATX and mATX form factors, so either is suitable. The only notable difference is that the Asrock model includes Wi-Fi, while the other models do not. Full ATX boards generally provide more PCI-e x1 expansion slots, though this may not be essential for you. Check additional features such as the number of USB ports on the back. Ultimately, choose the board that matches your aesthetic preferences. Good luck!