The AquaticLife fixtures seem to be a good combination of quality (not elite quality but better reflectors and other quality than many fixtures), price (not the absolute least expensive but definitely on the lower end of the price spectrum) and they are planted tank friendly (they offer freshwater combinations that include a good daylight (6000K I think) bulb and a roseate or pink grow bulb type bulb.
The Drs. have the 36" dual T5HO AquaticLife fixture in 36" for $120.
http://www.fosterandsmithaquatics.com/product/prod_display.cfm?c=3578+3733+22134&pcatid=22134
I just turned my 20" fixture upside down to double check the reflectors and while they are individual reflectors and look pretty good they aren't the full ridiculous mirrored parabolic reflectors. I am no expert but I would guess that they would sort of qualify as entry level when it comes to high quality individual reflectors. I can't imagine how it would be worth the effort to change out reflectors of this quality (though I can see how someone might need the extra intensity and would purchase super high end reflectors to start with).
I won't gaurantee it but I just measured the mounting legs and I *think* that if they were moved all the way to the outside on the 36" fixture you could fit them over the lip of a 39" tank.
These particular fixtures are also linkable so that you could hook the unit up with a second fixture but IMO if you had such a deep tank to require that you might want the two fixtures seperated anyways to cover more of the tank front to back.
The fixtures are basically drilled so that AquaticLife hanging mounts can be attached but they don't come with the actual clips or anything. I haven't looked into it to see how hard it would be to DIY a hanging kit for them so if you plan on hanging the light fixture you would need to either purchase the hanging kit from AquaticLife or figure out how to DIY.
For reference:
Not ten minutes ago I opened a GLO dual T5HO that I had recently ordered because a) they were out of the aquaticlife fixtures and b) the GLO fixture came with mounting hardware and more mounting options and I knew that I might end up with an open top tank.
The GLO fixture did not have individual reflectors and by the time that I bought the (not included) bulbs it ended up being about $30 more. The build quality looks and feels high but unless I turn the unit on and it is magically brighter than the AquaticLife by a significant amount I can't see as how I would ever recommend it over the AquaticLife fixture.