Two T5HO bulbs, using a good quality, full HO power ballast, with great reflectors, will probably give you around 120 micromols of PAR at 20 inches. Since the great reflectors approximately triple the light from the bulbs, that means you should get around 40 micromols of PAR without any reflectors. That is a bit high for a non-CO2 tank, but if you use Excel it might work ok.
What if I used regular T5? Would this be smarter? I could also install a T8 ballast.