As some of you may have noticed there is a strange limit in GPU frequency on RV670 based card.
The maximum stable frequency seems to be around... exactly at 862MHz...

I have seen some wild speculation about a driver problem or a GPU limitation.
All wrong.

Lets put it this way:

There is a mean bouncer standing outside of your favorite bar (863MHz).
Bouncer´s name: is PLL VCO Divider

The frequency of GPU internal PLLs are changing with GPU frequency.
At certain points the PLL must change it´s divider to maintain the frequency at correct range.
If the divider is not changing for some reason the frequency of the PLL will raise too high and it will flip.
This is what happening at 862MHz.

It is pretty much the same thing on cars.
To reach higher speeds you need to put in a bigger gear.

The problem can be easily fixed by updating the new bios.
Unfortunately I don´t have a bios for HD 3850 cards, but it should also be available soon.

HD 3870 PLL VCO Fixed Bios v010.071