Conclusions
Although three channels of DDR3 memory might seem excessive, the Core i7 really does seem to make good use of faster memory, at least in synthetic tests. But that was to be expected. The real question is whether those gains translate to real-world applications, and it's here that the results are more mixed. Certainly, in scientific computing tests like Euler3d and MyriMatch, which we already know to be sensitive to memory subsystem performance, faster memory can provide tangible performance perks. However, common desktop applications like those highlighted by WorldBench don't benefit much from higher memory clocks or tighter timings. Neither do most games, which at best show minor frame rate improvements that aren't significant enough for most folks to even notice, let alone appreciate.

Based on these results, the question of whether it's worth shelling out for fancy memory for a Core i7 build depends largely on which processor you're going to use and what applications you'll be running. If you have your heart set on a Core i7-965 Extreme and will be running applications capable of taking advantage of additional memory bandwidth, by all means splurge on some DDR3-1600 DIMMs. Sure, you'll pay twice the price of pedestrian DDR3-1066 modules, but anyone considering a 965 Extreme clearly doesn't have budget constraints.

Most enthusiasts do have budgets, though, and we're generally disinclined to swallow the exorbitant premiums associated with flagship gear, even if it is faster. I suspect most folks rolling their own Core i7 systems will stick with the Core i7-920. Unless you're going to push the base clock, which requires some cooperation from your motherboard, the 920 is essentially limited to DDR3-1066. At that speed, DIMMs with 7-7-7-20 timings are actually quite affordable and widely available, so there's really no need to settle for budget modules with looser timings. Our testing shows that you can even get away with a dual-channel config if you happen to already have a couple of DDR3 DIMMs lying around. I wouldn't skimp on that third memory module if I were building a Core i7 system from scratch, though.

Of course, many enthusiasts who spring for a Core i7-920 will be looking to overclock by increasing processor's base clock speed. Turning up the base clock allows for faster memory speeds, and given that the 920's memory bus multipliers are limited to 6X or 8X, you'll actually need DIMMs capable of running at faster than 1066MHz if you intend to push the base clock above 178MHz. Whether it's worth springing for DDR3-1600 modules over more affordable DDR3-1333 DIMMs will depend entirely on the applications you use and just how high you intend to push the base clock. You'll need to reach at least 200MHz to run 1600MHz DIMMs at full speed, and not every Core i7 motherboard is up to that task.

In the end, Core i7 processors will certainly achieve higher levels of performance when paired with faster memory, but you don't lose all that much—particularly with games and common desktop applications—by running slower, more affordable DIMMs. That's good to know for folks looking at the relatively high prices of fancy triple-channel DDR3-1600 kits. However, if you're going to overclock, it's worth having the extra headroom that faster modules can provide.