I noticed that most available processors only have 4 cores. I see people that have posted in the XPlane forums that they have more cores.....how is this possible?

The core i7 processor has a feature called HyperThreading (HT). It was a feature introduced back in the Pentium 4 days where a processor could do two things at a time, splitting it in half, like a single core processor acting like a dual core. The difference between the i3/i5/i7 is simply a feature list. i3 is a basic dual core processor with no TurboBoost or HT. The i5 is a dual- or quad-core i3 with TurboBoost (where when necessary, the processor overclocks ITSELF to a higher speed, i.e. 3.3gHz overclocks to a 3.7gHz when usage is high). The i7 is a quad core i5 with both TurboBoost AND HyperThreading.The one thing to remember is that you can save money if you don't plan on overclocking the processor by getting a non K series CPU. The K series i5/i7 processors have an unlocked overclocking multiplier which make it breeze easy to go from stock speed to higher speed without changing 120+ settings to get it balanced right. By K series, I mean i5-2500K or i7-2600K versus i5-2350 or i7-2090. Notice the lack of the K on the second set of CPUs. The won't overclock as well as the K series CPUs as they are not meant to.For raw graphics power, I'd go with the 580 as it is a better card numbers to numbers. If you're planning on building in a few months after XMas, you might do well to wait until around April when the new line of graphics cards are due out. It will drive down the price of the existing cards as well as give you access to the next-gen cards.RAM speed with the new intel processors isn't an issue, it really boils down to capacity. As long as you have enough RAM to run your applications, that's all that is needed. If you can get 1600mHz ram at half the price of 2000mHz ram, you won't see much of a difference, but the price difference could allow you to upgrade your video card or hard drive or buy a new yoke.The only thing you didn't specify was the operating system. Obviously a 64-bit OS is needed due to the high amount of RAM you'll be using. Plus, it appears XPlane will support this in the future which is an added "duh" when choosing the OS.

Im running a I7-860. Stock speed = 2,8 GHZ. The max OC i achieved was 3,9 GHZ without HT and all further CPU related options. With this config i ran Railworks 2012. To my suprise i experienced very bad frames. So i loaded the bios defaults and started over again, this time with HT on and all CPU related options. I came to a stable 3,5. And again i ran Railworks and i improved my frames with 10 or so. Its not just the max GHZ you can squeez out of a CPU. Its about stability (running a CPU stress test for several hours) and ofcourse the HT on or off. Remember when OC-ing.**edit**, i dont own Xplane yet. It will be available somewere in January or february in the Netherlands.

The Gen1 i7's weren't nearly as overclockable as they should have been. The newer Gen2 LGA1355 are much easier with the K series. There is a limit at which you have to start adjusting voltages to give the CPU the power it needs as the Motherboard won't give more than a set amount and the extra juice is needed to get higher speeds, but when I got my i7-920, I got it up to 3.8gHz on a board that others were getting 4.2gHz. The stability needed to run the computer as hard as we do just isn't there for the money. The new i5 I got up to 4.8gHz in a matter of minutes. No more fidgeting with timings and FSB and all the other 12 settings needed for an overclock. Just crank up the BClk to 48 instead of 33 and you just went from a 3.3gHz to a 4.8gHz. The other settings are all automatic. If I want higher than 4.8, I'll need to adjust the CPU Voltage, but why do I need more than 4.8 right now? So I'll leave that for a future free upgrade built into the chip I bought. When I need it, it can go even higher than 4.8. The i7 is the same story.