The latest version is 8.5.1. There are two varieties of it -- Standard, and Basic.
Standard runs under a Java framework so its memory and CPU requirements are twice as high, but the user interface is more flexible, incorporating things like composite applications, RSS feeds, calendar federation, etc. The Standard client includes tons of new configuration files for the Java functionality. Deployment of Java components follows a new model.
The Basic client has similar requirements to what you're used to in 6.5. The functionality is similar, although there are many nice new features added. The same workstation files you used in 6.5 are still there. Desktop suppport is largly unchanged, although the ID Vault server feature will greatly improve ID management.
Upgrading to 8.5.1 Basic will be easy. Supporting 8.5.1 Standard would introduce some new concepts.