FPS fall with Track IR 4 Pro and bracket SPOT view..?

I am using FS9 on a DELL XPS machine with eVGA 7900GTO card. I get very good frames and fluidity with all VCs using a single 24" LCD monitor and a secondary 20" LCD for maps, gauges, etc. But there are two conditions where fps can fall considerably and stay low even after I remove the "offending" circumstances.First, when I open a new SPOT view by using the bracket key on my keyboard in FS9, and then undock and enlarge that SPOT view on the secondary monitor to around 15"x15" or so, frames fall somewhat (not a lot) but the image generally remains fluid and crystal clear. If I am using a VC, however, frames can plummet at some point (especially with lots of clouds for e.g.) and then even when I close that SPOT view window on the secondary monitor, fps can remain low and there is a certain degradation of visual performance on the 24" primary monitor.Second, when I use the Track IR 4 Pro with dense and demanding add-on a/c, and I am in the VC on the primary monitor, fps can fall similarly and stay low even after turning off Track IR.I am puzzled by this. Why does this happen? Is there some sort of memory leak or what ? This seems to happen largely or only with dense, demanding add-on aircraft such as PMDG 744 and the CLS A340-500/600.Appreciate any tips or advice, thanks.JS