I honestly haven't heard anything about EPoX using poor-quality components in those boards. If they were, I doubt you'd be seeing so many positive reviews on them. None of them I've read have mentioned anything of the sort, for that matter.
The DFI board is great for extreme overclocking, but it does have some stability issues and needs very high-quality components to really work well at all. If you're a first-time builder then you may have trouble ironing out the problems. But hey, if you're willing to pony up the extra money to get the upgraded components, then go for it, I say! It may be harder to install, but there are a number of people not just on this forum but on others that could help you out with the DFI board if you wanted to go for it.
Unless I'm mistaken, EPoX's SLI board and their Ultra board should both be 1 GHz...the FSB speeds for both the Ultra and SLI EPoX boards are listed as the same on their web site.
With a setup like the one you were talking about, you'd have plenty of room for expansion later on. You could buiy another GeForce 6600 GT and turn on the SLI feature on your board for greater performance without breaking the bank, and you could always get another 80 gigabyte hard drive and set it up to work with your original one in RAID.
...do you have a case and a power supply? To go with a system like that, you need to have a sturdy, reliable power supply that is ATX 2.0 compliant. But it doesn't have to cost a lot - despite the massive power supplies out there that reach upwards of 500 watts or more, the most a tricked-out system would draw doesn't even come close to that. And for a system like yours, I'd look for a power supply that's around 430 watts or so, like this Antec TruePower 2.0, 430 watt power supply for $66.66:
And as for a case, well, you don't have to break the bank to get a great case either as long as you don't mind it being from a 'budget-minded' series. But it's made by Antec, and as anybody who knows anything will tell you, they make some really great products no matter which one you're buying.
You may have seen people making a big fuss about Antec's new P180 case since it's supposed to be the latest and greatest thing in cooling - and to an extent, it is pretty good at cooling. But you have to really tinker around with the airflow to get it to work right, finding places to put the cables is a nightmare, and you need to take two of the fans that are included out to get any benefit from it. The guys over at SilentPCReview.com, one of my favorite sites, did a side-by-side comparison of Antec's P180 and their budget-minded SLK3000b model. And guess what? The temperatures of the components inside the two cases were found to be within a few degrees of each other!
You can get Antec's SLK3000b from their Solution series from that web site for about $42. What you get is a reliable case with great cooling that is quiet, has good airflow, and is a terrific performer overall.