Semp, the ASUS boards, especially the "ROG" gamer boards allow you to mess with the OC settings in the bios from the windows environment. What MACE described is a very typical overclock of the 3570 for a decent, medium level 24/7 OC that is 100% stable, all done from windows. All that happens I think is that the software changes the bios settings for you, without having to actually "boot" into the bios. So actually "doing it in bios" like you recommend is already happening, although without actually "being" in the bios screen as it were.
As for the OP, I would go with the 3570 with a decent board/cooler and OC it, and spend the extra 100$ on a better video card. A 7870 won't give you 'glass smooth' video in all games, I can assure you of that. Load up even an older game like Napolean Total War, and put 8 armies on the screen at max, and a 7870 will chug. Like Brody and others said, go with a 7970, or even a 7850 which will easily overclock to 7970 performance levels. If not that, then a higher end 670 or lower end 680 evga card. That 3570 system with any of those cards will smoke a 3770 with a 7870.
As for the sound cards, I've always installed one, as it is an old habit from back in the days when you HAD to have one, circa the late 90's etc. I know that over the years that the motherboard manufacturers have made this not necessary with their high quality on board sound, but like Skuzzy was saying, it DOES take a little of the load off of the CPU in my experience. Is it enough to notice during regular PC use, no not really, but it IS there. Also, the card I use is the Fatality 3D one from Creative, and it comes with a nice little control panel that goes into your case front slot, if you have an empty one. For 130$, it may seem like money wasted when the on board sound is nearly as good, but when you spend 3500$ on a system with a 3960, a 690 video card etc, spending a little extra on a sound card isn't a huge deal. I wouldn't recommend it for a budget system, or even an enthusiast system that is "on a budget", but for bragging rights/guy who has everything type of PC builders, it isn't a useless option by any means IMO.
As for the whole blu ray license issue nonsense, I fell victim to this recently as well, when I used my old system after getting a new one as a HTPC - home theatre PC. I was so happy getting my new LED big screen, and setting up my PC in my bedroom, and thinking I had every possible problem licked, until I slid in a BR disc for the first time. Of course it wouldn't play, and even with the RETAIL version of a well known manufacturer's blu ray drive, I still had to purchase ANOTHER license in order to view BR, same as Mace. Ridiculous.