@Celegorm,
All excellent points, I'd be interested to know your system specs., because you obviously understand, and build to enjoy this hobby.
I purchased my GTX 580 cards, about a year and a half ago, when they were first released. I skipped the 680s, because for me, there wasn't a significant enough improvement in performance to justify the expense. Next year, my son will get these 580s because I'll be buying a pair of 780s for a 3 monitor system. I tend to purchase graphic cards every other generation for maximum life, and dollar value. Something the OP may want to consider when building his. I have not experienced "stutter" with SLI performance using a pair of GTX 280 cards, 460 cards, or 580 cards, and I've built numerous systems with those cards over the years. Perhaps I've just been lucky.
The PSU was also a good point the OP may want to keep in mind. It seems to me that the single biggest mistake most folks make when building a computer is purchasing a PSU for exactly their needs at the time of the build. I always suggest a 30% to 40% overhead on a power supply. Why?
First because components age, and any PSU will be reduced in performance by 10% to 15% over the course of a few years. Second, because it is ridiculous to have to buy a new power supply a year or two later, because you want to add another video card, or some other component, and I see that happening to people all the time. Always purchase a power supply with enough "headroom", so that your system can grow, the PSU can handle it, and it runs cool, and is never operating at capacity. Consider a headroom of at least 25%.
Always attempt to purchase a motherboard with a socket and chipset that will be viable for the next generation of CPU. I use the word attempt because that just isn't always possible. Although there is no such thing as "future proof", you always want to at least strive for that goal.
If it's within your budget, include an SSD for at least your OS, and most important apps. 120/128GB solid state drives are available today for less than $100, and have a dramatic impact on system performance. Always remember that backing up data is critical so always plan on at least one, internal or external HDD for back ups, and storage.
If you get into gaming you'll soon realize how critical cooling can be. Always use a full tower case if possible. Full size chassis generally provide much better airflow, than mid-tower cases, and the HAF 932 Advanced, is one of the highest air flow, coolest cases available. I would also recommend the Cooler Master Storm Trooper, however, after building the same machine in both cases, and running numerous idle, and load benchmarks, the HAF 932 was about 5c cooler overall.
As for memory, always try to purchase the highest density sticks you can. In other words, if you want 16GB of memory, purchase 2x8GB sticks, rather than 4x4GB sticks. If you want 8GB, then buy 2x4GB sticks, and not 4x2GB sticks. Why? Because the more you populate the DIMM slots, the less room you have for future expansion. Also, if you're like many of us, and you decide to get into over clocking in the future, the more populated your DIMM slots, the more the CPU memory controller is loaded down, and so the more difficult it is to achieve high clock rates with the lowest voltage.
CPU cooling is a whole other subject, but we've given you enough to think about for now.
I hope these tips help.
