Would I see a performance increase over my ATA 133 hard drive if I used an external USB 2.0 drive?

Both having the same RPM and size, I wonder. USB 2.0 transfer rates for a 500GB mybook are 480 Mbits/s (Max). The likewise ultraATA133 drive only tops out at a meager 133 Mbits.s (Max). This being said, if I use an external Mybook, as opposed to an internal hard drive... Will I see a significant performance increase over the ATA drive?