Since you're ocing you might as well go with the 6300 imo... I just went with the 6400 cause i wanted to get 400 fsb and run 1:1 with my ram... but if money is an issue the 6300 overclocked is your winner... or maybe consider the 4300, its suppposed to overclock very well.
You also might consider the 650i boards. SLI are the only ones out right now with more to come, and the Ultra versions are on their way. We know that the Nvidia chipsets OC like mad. Between the 2 you've listed it's quite the toss up but I'd say go for the DS3 even though I really like Abit. There is no guarantee what one will OC better, but I think people have a better experience with the DS3. Customer service kinda sux either way.
I went for the AB9 Pro using an e6600. This config works well if you use 800MHz RAM because you can tell the motherboard that it is in fact 533MHz and then raise the FSB to 400. This lets the e6600 get to 3.6GHz and then pushes your RAM back upto 800MHz. This keeps the ratio at 1:1 and does not put extra pressure on your RAM.
Found this ran very stable on my system and I'm only using air cooling (but very good air cooling).
Can't guarrantee that it won't damage your system though. I now run my CPU at stock speeds because it is more than fast enough and at least guarrantees that your system won't fry itself after 2 years.
Lastly, two of my friends have a similar setup but use the new nForce boards (one of them is using the striker), I have found that my cheaper board is more stable and runs faster (and cooler) than theirs for half the price.
They are both good boards. Look in my sig and you will see a similar system to what you are looking at. My Xeon is just like the 6300 and you can see my OC. You will probably be able to achieve a lower vCore than me, for some reason these Xeons love higher voltages depending on the ones you get. I would recommend the Xeon still because for whatever reason. When I was @ 2.8ghz and my friend with the exact same system except he has an X1950XT my 3Dmark06 score was better than his in the CPU area as well as overall and my super PI was marginally and when I say that I mean like half of a second better than his, but none the less it was scoring a tad higher and @ 2.80ghz I am able to run the lowest voltages the board allows for vCore @ 1.325v so the setup is really great for the price. I head about many problems regarding memory with the DS3 especially since my chips are Micron D9's so that is why I went with the ABIT. Hope this helps.
Just curious is to what you have your NB voltage is at since our FSB settings are very similar assuming yours is @ 425 fsb. And if you disabled all of the features of your CPU. I disabled pretty much half of the features and am @ 426 fsb with 1.45v on the NB (MCH) and just am trying to see if this is a safe setting for continuous use for the next 1 - 3 years (probably more like 1.5 to 2 yrs @ best, lol gotta have them upgrades!!!). Thx man!