Memory bandwidth correlates slightly with performance in memory-intensive compute jobs. It is an interesting data point which correlates with performance, but little more can be said until one tests actual performance on specific tasks in specific programs. The on-chip CPU caches generally do a superb job of mitigating the limitations of memory speed.
The chipset in the MacBook Pro (June 2012) has outstanding memory bandwidth, substantially better than 3 modules in the Mac Pro Westmere 6-core. This keeps the CPU cores humming efficiently.