Question about internal drive speed in original TiBook

[Bill Planey]

I have a 400 mhz original TiBook and its 10 gig internal drive just doesn't
cut it anymore.  I have an extra 20 gig Travelstar, but it is only 4200 RPM.
I don't want to open the powerbook case up just to find out how fast is the
one I have now.  Anybody know offhand?  (it is the original supplied by
Apple).

Will I gain any speed by putting this 20 gig drive inside?   What's the
maximum (drive) speed that the bus in this TiBook can actually put to good
use?

Thanks!

Bill