HotHardware take a further look at the Intel Core 2 Quad Q8400 CPU. Here's a bit:

Intel's Q8400 is basically a Q9400 with 2MB of L2 cache disabled. This fact was reflected in our tests as we saw the two chips keep pace with one another in almost every benchmark. Against the AMD chips we used for comparison, the competition was also stiff. While the Q9400 was the best of the bunch, the Q8400 definitely held its own. Also, we were very happy with the 3.92GHz overclock we achieved with this chip at only 1.36V.

For about $180, the Q8400 provides enthusiasts with an affordable upgrade option without sacrificing much performance or overclocking ability. There is approximately a $35 difference between the Q8400 and the Q9400. While both run at 2.66GHz, the extra L2 cache on the Q9400 does give it an small edge in performance. If choosing between these two processors, we suggest going with the less expensive Q8400 as the difference between them is imperceptible in real world situations and they should overclock to similar levels.

Overall, we like what the Q8400 has to offer. It has mass appeal for being one of the most affordable Intel quad-cores on the market. Enthusiasts on a budget can make use of the processor's overclocking ability, while mainstream builders can save some money by building a Q8400-based and enjoy the benefits of a quad-core powered system for a relatively minimal investment. Those looking to squeeze more life out of their existing socket 775 system with a CPU upgrade should also consider this processor. The Intel Core 2 Quad Q8400 is good value, considering its asking price.