To be fair making a partition on the interior of the drive and then running off of that probably would be slightly faster than accessing it across the whole disk. I don't know if the difference would be noticible.
Partitions CAN make a system slightly faster, as was said above. For me, I have increased the speed of my system by creating scratch partitions, so instead of searching for scratch space in applications like CS2 and Cubase, everything is written to a large, blank area. It sped up those apps a bit, but not the system in general...
A much more effective method of increasing performance would be to use two hard drives on separate channels (this means no master/slave setup, only master). Put the operating system on one drive, and your applications and home folder on the other.