I think this question might want to get moved by a mod to the PC Building section of the forum, but either way here's my thoughts on your question.
Also what is your intended use for this build? Gaming, editing, ect?
Both RAM kist will work as max board ram is 128GB. https://www.asus.com/Motherboards/ROG-STRIX-Z490-E-GAMING/specifications/
I own this board and run 32GB in a 4x8GB configuration also.
If your building to game, the difference in FPS increase with either kits clock speeds is likely only a couple of frames if they were equal in total GB. From my experience when I overclocked my G.Skill PC3200 to 3600mhz I only noticed an increase of maybe 3-4 frames. I prefer to find my builds max frame rate for the game and then lock it in to that so frame times and such stay as constant as possible but that's another discussion on per game basis. Secondly, depending on what titles you play, at this point in time, your unlikely to benefit from increasing to 64GB if your intended use is gaming. In the games in play, the only time I came close to needing more RAM beyond 16GB was with Arizona Sunshine on Valve Index highest settings, it's the only reason I run 32GB in my gaming rig tbh, found it to be possible precursor to needing more in the future.
So if it were me it's going to come down to asking myself these questions-
What am I going to be doing on this PC or what is the largest load it will run?
Is cost a concern?
Is brand loyalty a concern?
P.S. Good luck on finding the i9-10900K. Been selling out in under 15 min everywhere.