IMO/IME the T-5 bulbs work really well and you can get by with quite a bit less wattage. I know just about everyone always talks about the wattage needed for a certain plants or for growing plants, but in reality, wattage is not what grows plants, it's the light intensity and the spectrum colors that contribute to plant growth. The real bottom line is that if the plants get enough light, they will grow and propagate, you just need to make sure the color spectrum is correct for the plants and the light 'at the plant level' is sufficient.
IME, I have used almost every type of bulb there is out there... screw-in compacts, 'regular' aquarium t12 bulbs, t12 daylight bulbs, t8 bulbs of all varying flavors, and some t5 bulbs as well. I have currently set up 8 fish tanks... 7 of which are planted and most being successful. My most successful tanks have either compact flourescent or t8 bulbs of 6,500K color. None of these tanks meet the 'wattage requirement' so many people live by... but it is planned that way because I'm concerned about the amount of light, not the wattage!
Try an experiment. Replace a t12 bulb with a t8 bulb... what happens? More light... less wattage. You can do that with the same ballasts all day long with no problems. Since you cannot simply change to a t5 bulb, other changes are in order. I'll use my 55 gallon tanks as examples: I have 3 and these are my best planted tanks. All three have custom made canopies so as to house my custom lighting. The first one has 4 t8 6,500K Daylight bulbs from Home Depot. This is my best growing tank that readily has stem and vals reaching for the top. I should note that all tanks are on the same timer for 12 hours a day and use no Co2. I do add PMDD about every 3 days, about 1.5ml. This tank seems to be the brightest tank when looking at it, but has only 4x32W=128Watts total of light... just over the 2W everyone seems to want! The second tank was exactly like the first, but I needed a smaller top for it, so I switched it over to run 2 compact flourescent 36W, 6,700K bulbs, only 72 watts! This tank still does well, but growth is not as fast as tank 1. Java fern and anabius plants seem to do better in this tank, but there is also an area right in the middle that is 'shadowed' a little as the bulbs seem to project pretty straight downwards, not getting much light to the middle area. Stem plants still grow, but just not as fast as tank 1. The third 55 was set up from the start with 2 t5 bulbs. These bulbs throw out some real light!! I'm running the 54W variety on a workhorse 5 ballast ( same ballast on other tanks as well). This tank is almost as bright as the first tank at only 108 Watts total. I should note that these t5 bulbs are 10,000K as that's what came in the fixtures. The plants are growing great, but I think would do better with 6,500K bulbs and the colors would look better.
I know it is not exactly a carefully controlled experiment, but IMO, all three tanks are successful planted tanks. Bio-load is low on all tanks. I also have several smaller tanks, a 40 breeder and 2 20 gallons, 1 normal and one long. Lastly is a 75 gallon tank. All these others have different lighting experiments and some have done great and some not so well. The screw-in CPs really did well on my 20 'tall'. I then switched to running 2 18W compacts on it and things never changed a bit. I have 2 24" t8 bulbs on the 20 long and cannot keep the vals and chainswords trimmed enough! I believe this tank does so well because it is not as tall as most of the other tanks, so the light is not diffused as much when it reaches the plants. Even the anabius plants grow fast in that tank.
SO, to sum up all this rambling, IMO/IME it really depends on several factors, but I don't believe the 'wattage' rule really holds true for much more than standard t-12 bulbs. T-8 bulbs put out more light than t-12's and t-5's a lot more than t-8s. So that means IMO, you can use t-8 or t-5 bulbs and use less wattage. One thing hardly touched on is the height of the tank which I fell is very important. The light has to be able to reach the plants without being too diffused.
Last but not least, One so called aquarium lighting 'expect' who I have talked to at length and generally trust has said you really cannot consider the actinic bulbs wattage as part of the equation. Has to due with the single spectrum color or something, but he never included it with his tanks. FYI, he is a real strong proponent of running 5,500 K bulbs of whatever wattage he thinks is enough and then adds 1 or 2 true actinic bulbs to 'make up' for some of the colors lacking in the other bulbs. I will admit, his tanks look great and plants grow great albeit he takes much better care than I do!
So I hope all that helps, but I would say you could use some more lighting. Let us know what the test results are.
Best of luck,
BC
