!!!
Found a solution to raise up nTune Above 250MHz HTT!!!!!
Simply create a profile with 250MHz HTT and save it (like 250.nsu)
After that go to the profiles folder (user\AppData\local\Nvidia corp...\ntune\Proifiles) and copy the 250.nsu to an other name (like 260.nsu).
After that open the 260.nsu with notepad and edit it by changing the FSBMHZ value from 250 (or other value) to 255... 260.... 265....
I reached 2.6GHz stable with no problems..... at least for now....
Try it on..... it works!!! and it rocks!!!!!