i use inspector, so AA is not done through any FSX setting..
Perfect. So try the "override" instead of the "enhance" flag at the antialiasing options there and test again.
As said before, the Civa INS doesn't affect the fps at all but the handling of the antialiasing of popup windows (which is a global one for FSX) surely does.

Everytime i fly in the uk, and say, do a flight plan west,

the ins engages, and the heading selector will ALWAYS fix on north..

every time i reproduce it
I have no doubt that you can reproduce this behavior, but no one else can so far. That's an indicator of a system based or user caused error and therefor not a general fault (so far).
I'm sure we can help you here, on a user basis, but we need some information about how you get the INS ready for navigation and how you operate the AP and FD on the 707.

I also suggest to use and test the Doppler system first as this is the intended way of operating the 707. Captain Sim planned and programed her to use this while the INS is an optional thing.