1.9 ft high or long? If you have the height, you should definately go with the 400. That should provide ample lighting. If you have the money and the height, maybe 2x250s, or a 400, and a 250.
whats up buddha. you turned me on to this site and I like it. got a guy selling a 400 watter for $120 USD all of it is brand spanking new also. LINK; http://www.htgsupply.com/productdetail.asp?productID=518 don't think the link work so just cut and paste it. since it is almost 5' wide if you want any good results you have to go with the 400. you can drop alot of cfl's in there also but you will lose density on your buds. i'm probably gona say that your closet is 8' high since this is the usual height for a closet. as soon as you get your closet up and running you will have to think about odor. I would suggest a carbon scrubber and an ona block. that would do the trick nicely. got it in my house and when my mom comes to visit, BTW she is a minister lol, she suspects nothing!
4.75 feet is a little wide even for a 400. Get cardboard or plywood or something to shorten the length a little.
that 400 will do fine considering the measurements of his grow area. yes you are right about the 4'9" being too large for a 400. I would go with a sixer or maybe even 1000 with good vents but you are forgetting his width. it is only 2'. it would get too hot for anything much larger than the 400 unless he wants to pay out the ass for an induction fan. he might and I use the word might loosly, have an issue about lumen loss on the ends of his grow area, but he just has to throw a cfl on the ends and problem fixed. alot cheaper than buying a 600 watt HPS system. if he follows this setup it will yield 956 lumens per square foot if his light does not go over 6'. pretty good growing from my book. PEACE!