RTMA
DIY Fanatic
I would go 6 lamps with a 18" wide tank.. For t-5 more lamps mainly means more coverage.
Also look into the Giesemann Matrixx II fixture. I just replaced my ATI fixture with the Matrixx II and like it allot more.
+1
Here is my new Matrixx II Dimtec.

bulbs:
Blue+
Aquablue +
Super Act
Fiji
Blue+
Super Act
Gman Midday 6K
Blue+
FTS.
