You're right around the point they got renewed for two seasons at once, so they had a lot more freedom for extended plot/setting development. I forget exactly which two seasons they were, though.

If you're continuing and at all interested in the timing, SG-1 season 8 has a two-parter premiere, and Stargate Atlantis begins immediately after that, not before or at the same time.

I'd actually decided to re-watch the series this year and am just finishing the 8th season right now.