Just following up on this old thread. I upgraded to p3dv4 and the lag/stutters are not present any more.
Of course they aren't.
The scenery is very large so, if we didn't act aggressively on memory management, it would likely crash a 32 bit sim with an OOM so, I hope you'll agree that some stuttering is better than an OOM crash. With the Anti pop-up, you had a way to control this.
But under 64 bit, our software behaves differently, and is not trying to save memory at all cost so, the Anti pop-up defaults to the highest value, and all the object loading ranges are doubled, so they are not created/destroyed very often, which result in a smoother flight.
So, thanks to the flexibility of our software, you could got an immediate improvement of the existing scenery, without waiting for a scenery patch, since we just made the script that runs the sceneries behaving differently in 32 or 64 bit mode.