Okay. I repotted 3 plants into 3 gallon buckets and put them outside to get air. I tried topping one of the plants, not sure if I did it right, I just cut off an inch or two from the top above the 2 nodes (V shape).
the repotting will help, and i'm sure the extra light from outside is going to help them along. hopefully the nute burn won't be an issue anymore, but if it appears to be a problem you'll likely have to give you plants a good flush with distilled water. as snax was saying, make sure you've got at least 100w of light per plant or so otherwise once you bring them in to flower they'll be rather sad.
your plant size of six inches at 5 weeks is fine (I'm not sure where chiefton8 is getting the 3-4 ft number for plants grown from seed -- perhaps s/he's thinking of five weeks for clones).
i'm by no means a true expert in growing, but 3-4 ft tall after 5 wks of veg from seed is what i typically get. i'm not trying to show you up, or tell you you know nothing about growing, but 3-4 ft after 5 wks of veg really isn't unreasonable.
this picture here is one of my plants under 250w MH after 5 weeks of veg from sprout: