E5400 @3.5ghz vs E8400/PhenomII @ 3.5ghz

I've read conflicting reviews in which some say the extra 4 mbs of cache makes a big difference and some say clock speed is still king. I know the e5400 will pretty much lag behind clock for clock but how much of a real world difference are we talking about here?

The reason I am asking this is because I was able to get my new e5400 to 3.5 ghz stable on stock cooling and on the free motherboard that came with it (Fry's anniversary sale, e5400 + biostar 31g mobo for $79). Initially, I was going in to see if they had any Phenom II's on sale but the only one was a 810 + 780v mobo for 199, which I didn't think was worth it, so I settled on the e5400. Don't get me wrong, I think the e5400 is a killer deal and I'm amazed at how well it overclocks even on this mobo/fan but there's still that empty feeling inside me that says I'm missing out on the raw power of a phenom II.

Assuming I get a reasonable overclock of around 3.5ghz on an e8400 or a Phenom II 720be, is it worth the extra money to switch up to a faster processor?

Whatever the case, I can't picture myself with the current biostar g31 board as it only supports pcie 1 and I can't adjust the memory volts, which has already affected my system's stability a little (using 2.0v rated memo, board only feeds it 1.85)

I have 14 more days to return my e5400 purchase so if I see a good Phenom II deal within that time, should I just go for it?

The extra cache certainly would help, however the real world performance difference would probably be negligible. The phenom II 720be would be a good choice if you need to do plenty of multitasking/encoding. However, clock for clock the 720 would lose to either the e5400 or the e8400 in anything that wouldn't require more than two cores. If you already have the e5400, you don't need to upgrade to the e8400, however if you need the extra core, the phenom II would be a nice upgrade.

Great job on getting up to 3.5GHz. I'm not that familiar with the 5400, but I know you've done well if you can get the 5200 up to 3.0, let alone 3.5. (3.5GHz is pretty much unheard of with the 5200, at least on air/stock cooler.) The 8400 has more then just an extra 4MBs of L2 cache. It has the faster FSB (1333 vs 800) and an extra 300MHz.

Clock speed wise the 720 is right in there. (2.8GHz vs 3.0/2.7GHz.) It might not be as efficient clock for clock, but at least the clocks are close. What it does have over the other chips is the extra core. For tasks that like cores, this should help it to be faster. Whether you should get it however is hard to say.

You didn't give us one clue as to what you use the machine for. If your just surfing or light gaming, stay with what you have. If you do transcoding or heavy Photoshop use, get the 720. The extra core will help, and it will be money well spent.

"If it ain't broke, don't fix it" and "don't screw with success" You got a great deal on the CPU and mobo, they're performing great, drop the money in another area.