Looking to squeeze more performance out of my E8400 - please help!

the yorkfield would actually be a good upgrade for you if the price is right. most of those Q9XX chips tend to be overpriced and not worth the investment.

I also would not invest in new ram for two reasons
1. you won't get any more improvement past 4GB
2. DDR2 is rather expensive and outdated, never a good combo to invest in

can you up the fsb a bit more if you dropped the memory and pci clock multipliers?

I did some overclocking last night to squeeze more out of the E8400. Bumped the frequency from 400 to 430 and got it to stabalize at about 3.8ghz, roughly 1700 fsb. I was trying to get it to hit 4.0ghz, but it wasn't stable at all. Not sure if I need better cooling or something but I'm already using an aftermarket cooler. Perhaps I'll look into getting a better cooler and cleaning / applying new paste.

Another thing I was trying to do was change my memory timings from 5-5-5-18 to 4-4-4-12. Supposedly the memory could handle it, but I can't even get it to load Windows without BSOD. Memory runs at 1.8v and I bumped it to 2.0v, but still no stability at all. Only way I could load with those timings is if I left my CPU alone at 3.0ghz. Any idea why this would cause so much instability? And would that give me a noticeable performance boost? Maybe I should be happy with what I got and stop trying to blow up something.  

you want to move the other direction with your memory timings with your high clock rate. At 430 your memory is running at DDR2-860 so you want more timing delays , not less, to make it work. I would try 6-6-6-19 with 2T command rate

It all depends on if the game has be programmed to use all 4 threads of a quad core CPU. older games that are programmed to used only 1 or 2 don't get any extra help from having higher number cored CPU. these days new games are programmed to unilize all of the threads in a quad core. I personally have the Core 2 Q9400 because I couldn't get a hold of a 9550 anywhere so i had to settle. That being said, My Machine runs BF3 amazingly with the q9400, and i don't think you will notice a difference between the q9400 and q9550 if your using stock everything for games. I got my q9400 overclocked from its 2.66ghz stock to 3.2ghz. Im not sure if you can squeeze anymore power out of a q9550 or not. all in all if I were to be thinking about a new machine, I'd be building a brand new i7 machine.

Yeah.. the last few days I've been trying to milk my setup for what it's worth. Bought a CM Hyper 212 EVO cooler with an additional fan and some new thermal paste. Was amazed at how much of a difference that made! I was able to overclock my e8400 to 4ghz stable with it around 56c full load. I finally decided after all that though to just go with what I've been wanting to do for a long time now which was upgrading to a SB i7 setup.

New setup:

Asus P8P67 EVO Rev 3.0 MB
G.SKILL Ripjaws X 8GB (2 x 4GB) DDR3 2133 Model F3-17000CL9D-8GBXM
Intel i7 2600k
PNY GTX 570

Just waiting on memory to come in and will be swinging by MicroCenter tomorrow for my in-store pickup of the cpu  . For anyone looking to do a similar setup, Fry's Electronics is having an awesome deal on the P8P67 EVO (it's what jumped started me on this full blown upgrade). Currently the board is priced at $159.99, then a $30 mail in rebate dropping it down to $129.99! MicroCenter also has a great deal on the i7 2600k, $279.99! Memory was $89.99 through Newegg.com.

I can't wait to see how BF3 runs after this! Should be set for another couple of years  .

Now on to putting up my old setup on Ebay and use that to cover some of this cost lol.