I've been getting this issue for quite some time. For some reason, whenever I lift off, I get a huge decline in FPS and/or a large stutter - as soon as I'm about 25 ft from the ground everything is back to normal. This happens on takeoff and landing.Anyone else getting this?

I used to on my old rig. Not anymore (QX9650/4GB/Raptor). I reckon it's a bottleneck when loading more scenery after you gain height.

Try this out and see if it helps. Set the pre-Render Limit to 1 using NHANCER. It defaults to 3. When I changed it to 1 it really helped with that issue.