Windows 2003 & Windows 2003 R2

All my current servers were installed using the Standard Windows 2003 server CD about 3 to 4 years ago, before R2 came out. One of the servers is an Exchange server.

I am now going to replace two of my servers. NOT the Exchange server. My question is, should I use the Windows 2003 Server R2 cd’s or stay with the standard 2003 CD’s?

Will the R2 have any impact on my current domain? or the Exchange server? One of the servers being replaced is the DC.