IMO, you should either pay up for this AIO (which would probably just be enough to keep your 3900x from max temp under full load)So i dont need the 5.25 drive bay for an optical drive. I need the 5.25 bay to mount one of these:
View attachment 478002
Also, using a top-down style of cooler, even super low-profile, will likely see the bottom of this thing ^ as an obstruction to air flow and the RAM would probably end up baking under heavy load.
Or use a different, larger case. Which will allow a decent, more conventional heatsink/fan.