To answer your original post, there are very few differences between 670E and 870E. Technically, the only 'mandatory' difference per AMD is that the 870E series must have USB4 (psst, Thunderbolt) as standard, while it was optional on the 670E. Then again, you can get a nice 670E and put in an AIC for additional options. Most of my mobos (total ~ 20) are Asus ROG desktop and/or HEDT boards, with the odd Gigabyte and MSI. That said, I picked up an Aorus 670E Master last fall along with a 7950X3D and 2x 24 GB DDR5. That board turned out to be a fantastic performer...DDR5 8000 and beyond is no problem (have run at least 8000 since I completed the build). The system also has a no-sweat profile for 4x 24 / 96 GB CL30 6400 that works perfectly well when I ran it for a special LLM task. BTW, I had my 670E Master as high as DDR5 8600 with 2x 24 GB (via bclk, though)...great board for RAM oc.
I am waiting to see what the Ryzen 9950X3D is like in real-world testing - I will either add another Aorus 670E Master or pick up an Aorus 870E Master if I go for a 9950X3D instead of another option such as Threadripper Pro. The Aorus 670E Master and 870E Master are almost identical other than the faster network chip. The Aorus top boards like the 670E/870E Master also are among the few boards that can run R-DDR5 (full EEC memory) without any issue, and they also have bifurcation options - both are important to me as I tend to recycle my fun boards into productivity tasks down the line. I should mention that there is also the Aorus 870E Extreme coming out - it is like the Master (both support DDR5 OC to 8600), but the Aorus 870E Xtreme also has dual 10 GBE onboard and some other extras such as programmable LCD screens on the mobo. The only problem: It likely will be around $800 - $1k
So for me, the Aorus 670E/870E Master are the best choice, but the vid below has detailed a 21 board feature comparison review for 870/870E - a great reference piece.