I tried the development version and the FPS is much much better for me and a few other guys in the ZA community...
I could fly across the majority of Altis with very few minor issues for about 30 minutes before the same problem as mentioned above occurs.
Strangely it happens at any point on the island. It originally only happened when I would fly over a large town or when I reached 10 minutes of gameplay.
Something to be noted is that after running the game in windowed mode and monitoring my Ram resources, it seems that when it reaches 2.40gb used thats when the problem occurs.

Thanks so much for the feedback so far...

No problem... Please see attached