Hi all.  Ive had my 280 CLC for about six months cooling my old overclocked  1700x.  I recently upgraded to a 5900x drop in replacement.  Even at stock speeds and settings, I notice the CPU temps spike quite high.  Especially right after bootup to windows, or during single threaded tasks.  At stock settings, I see as high as 80c just by booting into windows.  EVGA flow control shows that my coolant temps are quite low, around 30c or so.  The pump speed is full, and fan speed is set to scale with coolant temps.  
 
Cinebench multi core will usually hover around 70c.  But single core tests will hit 80 or so.  
 
Due to the high CPU temps and low coolant temps, I suspected the thermal compound or block seating.  Ive reseated the block four times.  Ive used MX5, arctic silver AS5, and most recently thermal grizzly kryonaut.  It may have improved a degree or two, but not much.  The block is seated correctly with the D-style screws, same as I used on my 1700x.  There's not a ton of pressure on the CPU, but the block doesnt appear to be loose and floating either.  It seems t o have good contact.
 
Are 80c degree temps expected from the 5900x at completely stock settings with the 280 CLC?  Is there anything I can do to pull heat away from the CPU quicker?  With such low coolant temps, it seems like the 280 CLC should be doing a better job cooling this off.
 
Thanks for any advice.