sounds like P1/P2 is set to AUTO and being disabled. set them to ENABLED and you should see bandwidth numbers come back to life. after a certain FSB, AUTO disables them. P1/P2 are to the chipset performance that tRD is to Intel chipsets performance...and bandwidth is heavily determined by chipset performance.

of course, this also stresses the SPP more than with them disabled so you might need to increase vSPP and with vSPP increases the temperature increases too. this may result in instability despite higher voltages. i have found the SPP on the 790i to be very temperature sensitive. 10C off SPP temp going from the stock cooler to water really opened this board up. HTH