Intel Core 2 Quad

Verdict: These high-end processors deliver maximum performance, but at a heavy price.

The Core 2 Quad and Core 2 Extreme are the most powerful CPUs in Intel's line-up. As the name implies, Core 2 Quad processors all have four physical cores, while the Core 2 Extreme range includes one dual-core processor - the X6800 - as well as the quad-core QX6000 and QX9000 ranges.

Core 2 Quad

The Core 2 Quad range includes both 65nm and 45nm parts, based on the Kentsfield and Yorkfield cores respectively. Internally, they're effectively a pair of Core 2 Duo processors built into one chip. As AMD likes to point out, this is less efficient than the Phenom's fully integrated design, as cores on different dies can't communicate directly at the chip's full internal speed. Instead, they have to pass data back and forth via the slower front side bus.

The proof is in the results. The Core 2 Quad Q6600 costs just £4 more than AMD's flagship Phenom 9600, but includes 8MB of on-die L2 cache, twice the total available to the Phenom. This helped the Q6600 achieve a storming 1.45 in our benchmarks, while AMD's quad-core processor scored only 1.28. In fact, in our tests, every Core 2 Quad processor easily outpaced anything produced by AMD. That's partly down to bigger L2 caches (up to 12MB for the Q9450 and Q9550) and partly thanks to clock speeds that go as high as 2.83GHz on a 1,333MHz front side bus.

Yet as a desktop processor, the Core 2 Quad range faces stiff competition from Intel's own Core 2 Duos. The E8400, for example, achieved a higher overall benchmark score than the Q9300 in our tests, despite costing £42 less. The extra processing power of the Core 2 Quad only shines through in properly multithreaded applications, such as our 3ds Max test: here, the E8400 took 206 seconds to render a scene that the Q9300 completed in 156 seconds. But if you're looking for an all-rounder, the Core 2 Duo is better value.