I'm in s3e10 of SG-1. I've been binge watching SG-1. Should I wait until I've reached the season where Atlantis started (6?) or can I start watching it already? I'm too excited to wait for it as SG-1 has been excellent and want to start already! :)
Atlantis' season 1 corresponds with Sg-1's season 8. Sg-1's season 7 makes a plot point out of the search for the city of Atlantis, which culminates in an epic season finale that is ranked among the best of Sg-1's episodes. There are then some crossovers, most are minor to moderate. Although you will be seeing Sg-1 characters as they are after years of development.
Some people have watched Atlantis first and then went on to Sg-1. It's not the end of the world for them but, personally, I would recommend you wait if you're able as that is ideal to me. You'll just slow down your getting through Sg-1, which you say you're enjoying, and as an example of how they tie together, when you get to Sg-1's season 8 you will see them make two major operations to benefit Atlantis but you will have already known if they succeeded or failed from watching Atlantis' season 1.