Yes it's been a very productive 2 weeks, got quite a few things sorted.
The Atheros tweaking and taking a wee break from nV has given me a new lease of life and Forceware tweaking.
Bandwidth factor will have a different effect on different systems.
It's tied to the Memory clock and will change the Memory Clock (no other clock) to 3D low power setting if a certain amount of bandwidth gets exceeded for the given 2D memory clocks.
So for a go7900GS where the VBIOS with 100/100Mhz (c/m) the value of 5 will set raise the 2D clock to 300Mhz (3Dlow power setting) BUT leave the Core @ 100 Mhz.
With this setting the 300Mhz clock starts @ 1680x1050
Setting it to 6 lowers the point where begins, no use as it only uses more power than is need if a lower resolution is used.
And setting it to 4 doesn't set Memory clock to 300Mhz it before 1920x1080 (where the distortion begins)
If you set the Memory clock in Rivatune to 121Mhz (or 120Mhz in nTune) then the Bandwidth factor setting is no longer needed as the Memory bandwidth is high enough to handle 1920x1080 and 1920x1200.
A lesson in Bandwidth 101 (which coincidentally in Decimal = 5, this is scary