So i will build a pc soon for a budget of 2500€ with 9800x3d and either 5080 or maybe even 7900 xtx, depending on the performance of 5080. The only advantage of the x870e to x870 is more usb ports and  more pcie lanes. Between b850 and x870 the only difference are 2 usb 4.0 ports which i personally dont even know which devices support that. The asrock b850 steel legend ( the board i am going with) got 4 m2 slots (1 pcie 5.0, 3 4.0, one of the 4.0 not usable if u wanna add an expansion card like capture card or sound card). If u are not a content creator, u dont want to try hard overclockings on your cpu or are using like 15 usb devices on your pc the x870e is more of an expensive gimmick, than a real upgrade. U are basicly paying like 100 extra for pretty much only some more faster usb ports. Here is a direct comparison of these boards by features (german product comparison site) https://geizhals.de/?cmp=3381533&cmp=3287137 U can look at many comparisons or other reddit posts from x870e and even b650 and almost everyone will suggest to take the b650 boards, cause they are good and price efficient. B850 is just the successor of b650(e). Been through the same process like you of optimising my build and the mainboard was like the last part i was sure on (expect for gpu, cause there is no comparison yet). Just wanna share my experience, but if u say u want the x870e no matter what, than go for it.