Earlier PowerPC processors used the system bus to access both the level 2 cache memory and the main memory, which could result in conflicts. For example, under the previous approach, at processor clock speeds above 200 megahertz, the CPU would often stall as it waited for data to arrive from the level 2 cache. This enables the more effective use of level 2 cache, because even the relatively large amounts of data they can store can be accessed by the processor rapidly and efficiently. In fact, as clock speeds increase, so does the performance value offered by the backside cache design. On the first card below the cache is running at 150Mhz and on the second at 300Mhz.
Longer bar equals better performance.
I'm thinking of getting one.