I have used AH Supply's 55w combos before on a 55 gal. I would certainly have like a 75 gal much more (for aquascaping) but there are tricks in aquascaping to add depth (or the look of depth) to the aquarium. I decided to go with a 55 gallon I already owned and hang a suspended canopy about 12" off the water becuase I wanted to have floating plants as well. This was very easy to work around in the tank, and because I was fiddling with my aquascaping and plants so much, it ended up being a good call. I had 4" of FLourite substrate with a thin layer of peat below it, 4x55w AH combos in the suspended canopy and used 2 5300K bulbs in the front and 2 6500K bulbs in the rear. The display was great, and because I had Pressurised CO2 my plants were growing like crazy. I was getting $30+ each month in credit at my LFS for the clippings I was pruning out of this one small tank! She eventually cut me off, telling me that she couldn't sell the plants as fast as I would grow them! Many of my plants were very high light demanding stems, and they had great colors (sunset hygros and other reddish plants). The Water Sprite also looked great when you let it grow emerged. They get thin spindly and grow 8 inches or more out of your top. Their roots grow long and dense which is great for fish to hide in.
I really think If you want to go with a planted display tank, you won't be happy unless you get pres. CO2, 3wpg+ and a good substrate. A deeper tank is also a great feature for aquascaping!
