On all our tests Core 2 Duo E6750 performance was identical to Core 2 Duo E6700, even though it uses a faster front side bus – and we simulated the use of several different types of application.
So what is the advantage of using a Core 2 Duo E6750 instead of a Core 2 Duo E6700? Based on the results from our tests, none.
Then why Intel is launching this new 1,333 MHz external bus? We have two answers for that.
First, on quad-core CPUs the higher external clock rate may increase the system performance. This happens because currently on Intel quad-core CPUs the cores are arranged into two pairs. The cores inside each pair can talk directly to each other, but if they need to talk to a core that belongs to the other pair they need to go to the front side bus and make this connection going thru outside the processor. Increasing the CPU external clock rate increases, at least in theory, the speed each core pair can talk to each other. For a detailed explanation about this subject please read our Intel Quad Core Overview and Roadmap article.
We will have to wait until we review a quad-core CPU based on this new FSB to see if this is really the case.
The second reason we can see is regarding DDR3-1333 memories, which will be supported by the Intel X38 chipset to be launched in July. Using DDR3-1333 memories with a Core 2 running externally at 1,333 MHz you will be able to match the FSB clock with the memory clock, allowing you to achieve the maximum performance with current technology.
In retrospect we must keep in mind that this is the first time in six years that Intel is launching a new front side bus speed with memories matching it. When the Pentium 4 was launched, for example, it used the then-new 400 MHz FSB and there were no 400 MHz memories at the time – this was PC-100 times and DDR-400 wasn’t available yet. The same thing happened when they launched the 533 MHz, the 800 MHz and even the 1,066 MHz external clock speeds. Even to this date Intel chipsets do not officially support DDR2-1066 (even though Intel P965 and P35 can access memories at 1,066 MHz just fine and P35 officially support DDR3-1066). DDR3-1333 availability may be an issue, but that is a totally different story.
Source:Core 2 Duo E6750 Review