George, A concrete reason not to install 6.1 is that, according to Technote 1452146, "Databases that were formatted by a V6.1 server have DB2 9.5 tablespaces. Upgrading a V6.1 server to V6.2 does not convert the tablespaces. DB2 9.5 has limited capacity for releasing space to the operating system. ......Databases that were created with server V6.2 server define DB2 9.7 tablespaces with reclaimable space enabled."
Best wishes, Keith Arbogast Indiana University