Intel Core 2 Quad Q6600
The Core 2 Quad Q6600 was introduced in 2007. But there are still enthusiasts out there leaning on the quad-core processor even today, making this CPU somewhat of an anomaly in the fast-paced world of technological obsolescence.
Built on the revolutionary Core 2 architecture at 65 nm, and sporting a 2.4 GHz stock clock rate, the Q6600 hit the mid-3 GHz range without much trouble. That was amazing at the time, given the complexity of a quad-core processor.
Although it launched in the $850 range, the Q6600 dropped to $200 by 2010, making it popular with enthusiasts on a budget. By 2011, it was replaced by the Core 2 Quad Q9550, another CPU with a great overclocking reputation.
Intel Core i7-920
Intel's Nehalem architecture was introduced in 2008, accompanied by the Core i7 brand. Now, the Core 2 Quads weren't slouches. However, the successful re-incorporation of Hyper-Threading enabled the Core i7s to step performance up in highly parallel workloads. In addition, the LGA 1366 platform employed a triple-channel memory subsystem, with the controller built into the processor itself.
The flagship Core i7-965 Extreme (3.2 GHz) sold for $1000 and featured an unlocked clock multiplier. But the $285 Core i7-920 (2.67 GHz) offered an identical architecture for less than a third of the price. While it was multiplier-locked, the Core i7-920 achieved more than 4 GHz thanks to a forgiving BCLK. In fact, I continue using this processor in my main PC with no stability issues, a testament to the forward-looking Nehalem architecture and its X58 Express platform.
AMD Phenom II X2 550 And X3 720 Black Edition
AMD's flagship Phenom II was never an overclocking monster (effectively capping out in the 4 GHz range). But the company's Black Edition processors at least made tuning easier through access to unlocked ratio multipliers. The Phenom II X2 550 and X3 720 were extra special in that they contained disabled CPU cores that, in some cases, could be turned on using motherboards supporting this capability.
While some of these processors simply had defective cores that couldn't be resuscitated (making this a game of luck), a great many were able to operate as quad-core models, sometimes over 3 GHz. In 2010, when high-end quad-core Phenom IIs sold for $180, you could roll the dice for $100 and were often rewarded with a more premium-class chip. At worst, you had a dual- or triple-core CPU that could still be overclocked through its multiplier for relatively little.
Intel Core i5-2500K
Intel introduced its Sandy Bridge-based chips in 2011, built on a 32 nm process. Compared to the top-end Core i7 CPUs, the Core i5s lacked 2 MB of shared L3 cache and Intel's Hyper-Threading feature. Neither of those nips made a huge performance difference, except in heavily-threaded workloads.
On the other hand, the Core i5-2500K included an unlocked ratio multiplier, making it possible to push the stock 3.3 GHz CPU up as high as 4.5 GHz using air cooling. We considered the $225 price tag reasonable, considering the chip's high potential performance. Even today, relatively meager gains from Ivy Bridge and Haswell make the -2500K a strong choice for mainstream enthusiasts.
