Yeah, XFX suppose to be good, but I wonder what happened to them, I saw many complains about their tech support lately, but XFX cards is still decent. I haven't heard much about sapphire tech support, they are I think decent, but had some issue to, but like XFX sapphire cards are decent cards. So overall no difference, just choose the one you like most. MSI and ASUS with DCUII or TFIII (or even TFIV possibly, I saw somewhere (I think techpowerup) that MSI is going to release TFIV model of the 7800 and the 7700 series under the name 'Power' or 'Hawk') would also be a good option too.
Some of the 'OCd' or 'Superclocked' has only got like a few extra MHz with them. Although, they'd be more stable and you won't void your warranty if you try to OC as well.And they have more performance with them.
Well as others have said, I would have to agree that Sapphire, MSI, and HIS are the ones to go for. Gigabyte is pretty good too. Asus is so so, their direct cu have some issues, like on the hd7950. If you can try getting a non-reference model that runs really cool, that will allow you to overclock it well, but in general the hd7000's run pretty cool in general.
LOL at that card, made my day . The superclocked or OC cards has higher clocks compared to the reference clocks, whether the difference is a Hz, or 200Mhz. Yes they are faster than reference clocked models, and usually has better cooler and design, but they are not 'significantly' faster. As far as I know they can overclock better (little bit better) than reference clocked model because of the better cooler and design, but, should also be not significant either. About warranty, not sure but Gman450 says it has better warranty...
In my opinion, if the price of the superclocked/OC version is more than $10 higher, and you want to overclock the card yourself, and, you are sure that they don't have better cooler and design, there is no reason to get the superclocked/OC version of the card.