The 5200 does not have 2x2MB cache. 2MB total, its not a quad chip.
Nice list, but you didn't tell us what the budget is. You might not like my idea, but it is the best. Drop the stuff you don't NEED and buy some good stuff. I'll take the 250GB idea farther, don't get a harddrive at all. If you already have a 500GB and a 1TB drive, you don't need another harddrive. Burn some stuff off onto DVDs like everyone else. You can't keep EVERYTHING stored on your computer forever. Next, if you still need money, don't get the speakers. Yes it will suck, but hopefully only for a year or less while you save up the whopping $24. Last, if you have to, drop the video card down a bunch. I mean a lot. Get something dirt cheap. All of these items are easy to replace. Adding a hdd is simply, plugging in new speakers is a breeze, taking out a 9500GT and putting in a 4850 is also pretty simple. This last idea does add some total cost, so try not to do this.
With the money saved, you should be able to buy a good motherboard and the 5200. I would also like to point out that you probably need to buy a PSU. You have inflate prices, and are trusting your build to a 420W PSU that comes with a $49 case? If you value your electronics, this needs to change.