so i've done a bit of reading about how effective memory speed is calculated and such. I understand that the speed reported by GPUz should have a x8 applied and that the speed reported by MSI afterburner should have a x2 applied to it.
 
My card is the 1080 FTW2. pre-bios update it was reporting:
GPUz = 1251MHz (x8) = 10008Mbps
 
but MSI afterburner lists the speed as 4500MHz (x2) for 9000Mbps?
so i thought it was something with MSI, checked the EVGA XOC, same thing. huh?
 
ok so I updated the vBIOS to the 11Gbps on both the Master/Slave. and i'm seeing the same odd readings.
 
GPUz = 1376 (x8) = 11,008Gbps
MSI = 5005 (x2) = 10,010 Gbps
XOC = 5005 (x2) = 10,010 Gbps
 
so what's the deal here?

Yep, that is normal. Loads such as running folding@home will cause it drop down in speed.