Seagate Barracuda IV vs. V

[K Peex1]

Can anyone explain the differences between the Seagate Barracuda IV 
model (Manufacturer Part# ST380021A) and the Seagate Barracuda V model 
(Manufacturer Part# ST380023A)? Both are 80 GB.

And does it make any difference to our Cubes? I assume the difference 
is Ultra ATA and "non-ultra" ATA?

Did Seagate ever make "special edition" Barracudas with an 8 MB buffer?

Dell home has the IV 80 GB for US $83 and the V model for US $88 with 
free shipping.

Thanks for any help!

Kevin