IMO, lighting needs need to be figured by lumens per sq ft rather than watts per sq ft. Different types and sizes of lighting vary so much in their lumen to watt ratio that it makes using watts per sq ft an inefficient method of determining light needs. For example, CFLs emit around 62 lumens per watt. Two thousand watts of CFL is only 124,000 lumens--less than that of a single 1000W HPS and far below what this room requires. Two thousand watts (62.5 W per sq ft) is only adequate if the lumens are there.
The smaller HPS only put out about 100 lumens per watt, while the larger ones put out 150 lumens per watt. Since we define lighting needs by lumens per sq ft, that is really the best way to figure your lighting needs.