I don't think you'll notice any performance difference between a 7200, 5400, or 4800 rpm drive because the MPC will only be using the drive for storage of samples and data, not reading from the drive directly during sample playback. Now, if Akai adds multitrack recording and playback in a future OS update, OS 2.5 maybe???
( jk on that )
So, at this point, I wouldn't pay more for a "fast" spinning drive. Likewise, cache sizes shouldn't make a difference.
Just note that some notebook drives are 12mm height and those will not fit. Most notebook drives are 9mm height, so no worries with those.
And, anyone still curious about why you might want to buy an external drive enclosure, keep this in mind. The MPC1K transfers via USB 1.1, which is a _slow_ transfer rate. Transferring GBs of data will take forever.
Putting the drive in an external enclosure that supports firewire or USB 2.0 will allow you to transfer large amounts of data, GBs, much more quickly.
However, this is only true if your computer has firewire or USB 2.0 ports on it!! If you're using an older computer that only has USB 1.1, the external USB 2.0 enclosure will only transfer at the slower 1.1 speed.
If it's a desktop, you can usually add a firewire or USB 2.0 card to it. All Apple computers have had firewire standard for well over 5 years now, so no need to add anything if you get a firewire enclosure. Other folks will need to check their manufacturer's specs.
damn, that ended up being a lot longer post than I thought!!