nevermind, just re-read your post. If you are doing two plants get a 180 it will rock them out hard. Sorry - I pulled a wake and bake today, not firing on all cylinders.
I think the 180 would serve you well, but if you're using soil I wouldn't rec putting any more than 2 plants under each, you could get three in if you're using hydro. If you're planning on more than that get the 260. I've got a 250 (2010 model) it is beastly.