How high can i stably oc my core 2 duo e6550

wow thats epicly bottlenecking a 260... the answer to high you can fly is dependent how much rocket fuel you have in the jet pack ^.^

basically, it depends on a ridiculous number of factors, none of which we can reliably predict. if the mobo and RAM are not limiting factors (which the mobo most likely will be) then it comes down to the CPU's tolerance of FSB, and how high you're willing to push the vcore.

and add a healthy amount of luck to that, and you end up with no freaking idea! just test it out yourself... we can teach you how to do it but theres no way to know how far it will go. every chip is different.

two of the best answers I have read all year. Ok, so this is my first time in the forums this year; they are still funny answers.

Make small changes (ie: bunp the cpu to 2.5ghz for your first try) and leave teh vcore alone. If your system boots then run p95 for 1-2 hours. If everything is still good bump the cpu up a little more. Keep detailed notes of your settings so when your system fails to boot you can go back to your previous settings and add voltage or lower the frequency.

To summarize, small adjustments, take detailed notes and then test. Make sure you monitor temps as the cpu might boot but fry itself if you are not paying attention.

Like they both said above, every system is different so results are completely up in the air until you start the process.

Unless you are planning on using SLI, I would advise against another nVidia based motherboard.
They have to many issues including overheating, very poor overclocking, random data corruption, low USB transfer speeds, lower reliability compared to Intel based motherboards, ect.

I would recommend you look into an ASUS or Gigabyte Intel P45 based motherboard like the Gigabyte GA-EP45-UD3P for $116.99 after MIR.
This will give you a much more stable and generally better performing platform which has excellent overclocking abilities while saving you some cash at the same time.
Using a P45 based motherboard, you are basically guarantied a 2.8Ghz overclock and can probably push it much further.
With the 780i based motherboard, you will have to be very lucky to get it stable at the 400Mhz FSB required for a 2.8Ghz overclock.