And now for some other boring calculations:
Memory read (real) 9200mb/s
Memory Write 8500mb/s
L2 Cache read 24800mb/s
L2 Cache write 18070mb/s
Theoretical memory bandwidth is 25600mb/s
So if the memory is writing to CPU cache at speed of 9200mb/s CPU can write to the cache at approximately same speed and in next step the data are exported to the memory at same speed.
PCI-E can send data to memory at speed of 6700mb/s, however my current harddrive can read data at speed of 750mb/s. Since the memory has such wide bandwidth CPU and PCI-E can write at same time with speed 8500+6700 mb/s
Standard system bandwidth is fluctuating from 750 thought 6700, 8500 and 9200mb/s, but the system still has potential of lower the bandwidth differences. Current average bandwidth is 6200mb/s. Much better harddrive, and bit PCI-E overclocking can grant average system bandwidth around 8100mb/s.
So... E7500 vs Q9550 will have exactly same Memory read in everest on FSB 400. Also the Memory read will remain same no matter 800Mhz memory or 1600Mhz. Whats the difference?
Memory bandwidth should be at CPU bandwidth + PCI-E bandwidth. At 400Mhz fsb its 12,8gb/s + 8gb/s. This configuration allows to write from CPU and PCI-E simultaneously. The lowest memory frequency at this FSB speed is 1280Mhz dual channel to comply, while 1600Mhz will improve performance only because of its synced frequency. Beyond 1280Mhz of memory speed is no measurable improvement.
Why not to set the memory frequency to 800mhz? This will be enough for CPU only. Concurrent actions from CPU and PCI-E at the same time can mean lowering of total bandwidth to half - 6400mb/s.Range of memory frequency between 800Mhz-1280Mhz at FSB400 will mean performance improvement in matter of lowering bottleneck at memory subsystem and thus lowering probability of memory overload.
Most tests with GPU-z and HD 5850 1gb also show that Video memory is not utilized much. For games like Deus EX its mostly 50%. Skyrim uses up to 90%, but video memory dedicated from system ram never crossed 200mb. Therefore even 3D engines are running fine. Constant data stream from DVB-T tuner to graphic card can therefore cause system to fail more likely than 3d engine.