It will only increase performance in the case that you describe--lots and lots of small sized files.
For large files--ie, video editing, game texture processing, running programs, swap files--there you will take a hit.
As for the rest of it....you may be comparing apples to oranges...what's the buffer size on each drive? What's the average seek time? Burst time? How many platters? There is A LOT more that goes into determining a harddrives performance than RPMs and cluster size.
Granted, the smaller RAID cluster size (the usable chunk before the computer switches to the second physical drive) may be more efficient, but then you have the Windows format cluster size on top of that (which in NTFS is 4k, I think).
You may be chasing after performance that just won't be there on a notebook.