I'd recommend going with 8.3 or later. The differences in 8.x and 9.x are too much to post. Here's a link for reference:
Update: Gilgalidd, I didn't even know I did that till you pointed it out, LOL. My bad. Link updated.
Message was edited by: Knox - CCNP, CCNA Security
If you go forward to CCNP security, you'll want to work with both 8.2 and 8.3.
9 isn't on the tests as of when I took them.
A list of new features in v.9.