was rather skeptical when I bought KLAX, for pretty much all FSDT airports I have perform, not that good at all. KLAX, however, performs outstandingly, given the detail and size of the airport.
Even if KLAX performs better in relative terms *considering* its size and complexity, it should run fairly similar to our previous sceneries in absolute number ( =fps ), maybe only JFK could be slightly worse, but not of course because of it, rather the fact it lies in an area that's already very slow on its own.
But it might depend on your system: if you have a very strong CPU/RAM combination and an average video card, I guess that older sceneries like JFK or KORD should run similar to KLAX, but on a powerful video card, KLAX and KDFW will shine, because they make heavy usage of FSX materials with Shaders, so they rely much more on the video card, and don't contain any FS8 legacy code, which is instead more heavy on the CPU.
On such system, KDFW should perform good too, always keeping in mind the relative sizes: since KDFW is even larger than KLAX.