As ElDiabloConCaca mentioned, raw speed is not always better. I used a loaner ThinkPad for a month once. My experience was the interface was quicker on the PC, while processing files was inconsistent. For example, I enhance music files (Dead Shows). The PCs performance on each file (song) was unpredictable. The PC would start quickly or slow, would either continue quickly or slow until it was done.
My PB, although the interface may be a bit slower than a PC, its ability to process files is consistent through out. When I am enhancing a music file, not only does it allow me to have a sense of prediction (time), it efficiently completes the task. Each file (song) I deal with takes the same amount of time to complete as the last one did.