FPS drop during short final approach

Captains, So far I've been very pleased with the frame rates with the NGX - it's nice to be able to get at least 22-30 frames for most phases of flight. I have noticed, however, that there's a peculiar drop in frame rates that beings during the final phases of approach in the VC. During my approach and flare, I find that a smooth 23 FPS approach drops down suddenly to about 14-15 and the stuttering begins. Has anyone noticed this? I wonder what process in FSX or the NGX may be causing this. I noticed this flying into CYYC a few times - getting great frames up the threshold, and then a decrease. My taxi in also tends to be affected - the frame generally seem lower than they would be given the traffic/weather etc. I know it's fairly general, but I am interested in opinions/insights... i7 930, OC 3.3 GHz, 10 GB RAM, nVidia 465GTX (with PMDG sticky Inspector tweaks)REX 2.0, ASE, EzDoc, *******' tweaked FSX.CFG, external frame limit (=30)Most sliders to the right; AI traffic @ 20% Regards,Sam Kharey