DOUBLE WOW!
This is one of the more accurate description of what a Parhelia card can practically give a FSimmer! I have been browsing the Net for FS-relevant information regarding Parhelia's 3D performance, and here I see that you use the same addons which are "dear" to me, including the UT. I imagine that you spend quite a while around the EGLL where UT traffic can really bring any system to its proverbial knees.
I am encouraged by your "double digit" performance under these circumstances, so Parhelia is back on my nice-to-have list.
On the dual screen however, please accept a hint. You are perfectly right when you say that there is a parallax problem, but that can easily be solved (partially) . You just display the forward view in the "left" monitor and the forward-right view in the "right" monitor. Of course that might pose a problem to the person sitting in the 1st Officer seat :-), and won't solve the monitors gap problem, but this is as close you can get without spending $$$ on a collimating display. BTW, you should use the same trick with the Parhelia, with the added advantage of a wider field of view.
Best,
Al