You should be okay. I used normal flourescents on my 180 which is 24" deep and had no issues. Plus, it was hung 6" from the surface. I know that the t5 are a lot more powerful than the tubes I used which were 8X30w for 240 total........However, I had an open top which helps....
Remember that your substrate layer will take 1-3" as well so you make up a bit. Glass tops must be kept clean if used. Shading from maturing/growing plants is also more of an issue for the bottom plants and leaves at the bottom of stem plants when they get thick.
You can use anubias and crypts at the lower levels. Clear water also helps lol
Also depends on what plants you have and their placement.
I used a lot of Java fern, moss, anubias, and crypto before I switched to MH at 3x150 6500k
I think you will be okay for most applications.