Evidently, the i3 has changed a lot in performance since my two versions, both 1st gen models, one a mobile version (i3-370M). First, there's the lack of Turbo Boost on today's i3's, secondly it's not a quad core CPU, though does have H/T available. Kind of like showing up at a gunfight with a pocket knife.:lol:
Finally, the i3 of any type won't fit in the socket of that MB, limited to Socket 775 CPU's. That's what the OP has to work with, therefore the Q9650 gets the nudge, if the tower PC version, there's two, maybe three Extreme models, yet these likely costs more than a new i3 would. Though would be way too much for the SFF to use, the CPU alone would be using over half of the PSU's max power output, and no room for the 3rd party cooler that would be needed.
I say it's reasonable to go with 8GB DDR2 RAM, and an Intel Core 2 Quad 9550-9650. My PC of the same model has 8GB RAM & Intel Core 2 Duo E8400 running at 3.0Ghz. BTW, am on the PC, so will post a shot at my specs. Note that I did at one time also had the OEM GPU from my XPS 8700 in here, using a low profile bracket, but when my Optiplex 780 arrived a couple of weeks back, dropped it in there, which has the Q9650. Speccy specs following.
http://speccy.piriform.com/results/zqDhlH2yVfzJsLG5w8Lrvn8
My main issue with the E8400 isn't that it's a totally bad CPU, it's that when the PC sits for 2-4 weeks and not booted, everything wants to update/upgrade at once, and this is having Windows Update set to notify only. The result is the PC will freeze, it's best to leave alone for 3-5 minutes, even with a SSD installed. Try opening a browser after boot, it'll surely hang. Not so with the Q9650 & likely the same with the Q9550, that's the purpose of the quad, to multitask with minimal slowdown & that applies even in the year 2016.
The Q9550/9650 aren't modern by today's standards, yet look at the massive (& crappy) mobile market we have today, an i7 (& not a true quad core) 16-18W (or sub-20W) CPU has zero chance at outperforming either of the legacy models (& some 1st through 3rd gen i5 & i7 mobiles). Though the desktop CPU's are a different story, the i7-6700K is a killer CPU, and the i7-4790K (my next upgrade) isn't far behind. The i3 comes close to neither, nor the i7-4770 in my XPS 8700 that'll soon be sitting in a box.
This Topic has some meaning to be because of one reason, I have the very same PC, in fact, quite a collection. Would love to hear from others if any of the Q9xxx series were performed and the outcome.
Cat