If your aim is gaming, drop to a cheap 8G kit (2x4G) of 1600MHz DDR3 (if you overclock) or 1333MHz DDR3 (if you don't). Most games don't come anywhere near needing 8G of ram, let alone 16. And I don't think I've seen over 4G from general usage (including some compiling). If you know you'll be using more than 8G for some large task, it would be a different matter, but you say gaming is the most taxing thing you'll do with the computer. As far as specific kits,
this is what I've got, don't pay more for fancy heatspreaders or tighter timings, it's not worth it for Sandy Bridge, especially if you're not overclocking. That'll save you $60.
I'd also drop the 2600. The only real difference between the 2500 and 2600 is hyper-threading; again, games don't generally use more than 4 cores anyway, so it's 2-3% faster for about 50% more money. Should save a good $90-100 here, if you're overclocking get a decent heatsink for the CPU with some of that (Coolermaster Hyper 212+). To repeat again: You can't overclock the 2500 or 2600 chips, you need the 2500k or 2600k; if you want to overclock then spend the extra $10.
As far as the hard disk goes: The 5400RPM drives are slow, I'd try and get at least a 7200RPM drive for your boot/applications. However, I'd recommend instead getting a 60 or 64G SSD (I'd recommend a Crucial M4, or possibly a Corsair Force. The intel and Samsung 830 drives are good, too. Avoid OCZ if possible); install windows/applications to that, and put games/media/large stuff on the slow hard disk. A 64G Crucial M4 is $109, put the extra money towards a better video card. I would recommend a 6950, if you can fit it into the budget (they start around $220), or a Geforce 560 Ti if you prefer the green team. You won't need the versions with 2G of video memory for a 1080p screen, so don't waste the money.
In summary: For gaming, the video card is almost always the limiting factor, and hyperthreading/masses of RAM is pointless. For anything nonintensive (general use, documents, etc), hard disk access time is often the limiting factor, and an SSD makes everything outside a game feel faster. Save money on the CPU and excessive amounts of RAM, and spend it where you'll notice it.
Last thing: Case. I built a system inside one of those cases last week for a friend, was fairly nice to work with. The tool-free drives were fairly simple to work with and worked well, though I don't know how well they'll cope if you're swapping drives a lot.
