Sorry Lucas I have been out of pocket. The i5 750 is pretty anemic when it comes to running FSX the i5 870 would have been a better choice, but overclocking the i5 750 will help.
I did a complete write up on this overclock at Overclockers Club as did Tacohunter but can't find it right now so see if this helps you.
The P7P55D's overclocking settings can be found under the AI Tweaker tab. Before you can start overclocking, however, you'll need to decide which "Overclock Tuner" you'll be using. The first choice is manual, which will only allow you to increase and decrease some of the minor settings. Next up is auto, but that will just keep you on the auto settings. This isn't any fun, so most users will be using one of the next two options. D.O.C.P. and X.M.P. are the choices that will give you a slightly better overclock potential. I prefer D.O.C.P. because it gives you the most control, but some users may not be looking for this. In D.O.C.P., you'll be able to adjust BCLK,
[COLOR=#289E28 ! important][COLOR=#289E28 ! important][/COLOR][/COLOR]and CPU Ratio, and memory parameters. XMP will automatically set the BCLK, CPU ratio, and Memory parameters. In other words, it's pretty much like the Auto setting. When in D.O.C.P. mode, you'll be allowed to choose a DRAM OC Profile. This will automatically overclock your memory, but be aware it will lower your other settings to do so. I suggest leaving it on whatever speed your memory happens to be.
In the A.I. Tweaker set your DRAM Profile to match the mhz of your memory(you can raise it later if you want to) then set your CPU ration which is basically the same as a mulitiplier.
In other words, multiply your BCLK by your CPU Ratio and you'll get your CPU speed. You'll be able to increase the CPU Ratio to 21 by pressing the + button . If you're looking to lower the CPU Ratio, you'll need to hit the - button. Both Intel SpeedStep and the Xtreme Phase Full Power Mode can be enabled or disabled. When overclocking, I'd suggest disabling SpeedStep, but to try the Full Power Mode enabled. The latter will supposedly get you the best possible overclock for your CPU. More importantly, it will disable the EPU's auto power saving feature. BCLK is easily increased by pressing the + button on the keyboard, and decreased by pressing the - button.
DRAM Frequency can't really be changed unless you're increasing the BCLK. That's right, there's no longer a changeable memory multiplier. You will, however, be able to select between three speeds for each given BCLK. I found that selecting a lower speed didn't really help overclockabilty. In other words, if you can run your memory at the faster speed, run it at the faster speed. You'll have two different choices for the QPI frequency, and four different choices for the CPU Differential Amplitude. Adjusting the amplitude has the possibility to increase overclockablity, so I'd suggest trying out a few different settings when overclocking.
Much like amplitude, different Clock Skews may help increase overclockability. If you've got a lot of time on your hands, feel free to play around with different settings and see which works best for you. To adjust the voltage, you'll have to choose between doing it manually or offset. I prefer manual, but in both cases you'll be increasing the voltage with the + button, and decreasing it with the - button. The IMC voltage can also be adjusted. Again you'll be using the + and - buttons to do so.
Play with settings until you get a stable configuration.
Make sure your PCI-E setting is at 100. You should not have to overvolt to get to 3.3 maybe even 3.5 which should be enough to run FSX very well. Once you get your overclock right and tested then mess with your bandwidth multi inside of FSX until your CPU speed and GPU speed give you solid frame rates.
If you need more help let me know
Ted