Saving it for Lumia 1000. That's the only reason I can think why they named this phone 920, because they have a plan for later. Just a thought.
That's not really how Nokia names it devices. I said this already 3-4 months ago when people where guessing the name to be 1000 or similar.
Nokia's next flagship just might be Lumia 915. It's just the first digit that tells in what category the device belongs when it's released. It was the same in the previous two naming systems (xxxx and the different lettered series with two digits after it).
As far as quad core goes. Will Apple actually release quad core device? I personally think they will just go for the Nvidia style of crap and say the GPU has 120 cores just for marketing, like they did with the new iPad.
In a same time the new iPhone will run around the quad core Androids.
All of the manufacturers seem to be using the same exact SoC (MSM8960) on this first WP8 wave. Thankfully i have no seen complains about the specifications of Lumia 920 and ATIV S, even from places like Engadget as far as the core hw goes.
MSM8960 in the end is very capable SoC that has done great against the likes of quad core Tegra 3. Just like on iPhone the performance this kind of fully optimized SoC for the OS should be big advantage for all of these first wave WP8 devices compared to Android, no matter what they have inside.
Again, people are not complaining about GS3 SoC (in USA it's the same MSM8960 as on WP8). They certainly should not for WP8 that will actually use it to it's fullest.