The PAR @ 24"? Great!! A lil after 24 inches is where you see some significant drop offs but to give you an idea I have a 20" tall and Im keeping acros,digi's, encrusting SPS on the sand and a few inches above with exceptional growth and coloring.
True blue, or blue+? True blues dont have the PAR that blue+ do that incorporate some of the actinic and daylight spectrum in there bulbs. Without the reflector though T5's are basically a High Output compact. But the reflectors is what sets these bulbs apart from the rest of the crowd.
Life span? If you overdrive them with an Ice Cap ballast you can bank on the life being anywhere from 9mos-1yr keeping optimal output. With a normal ballast , Triad or Workhorse you can expect a year to 1&1/2 years with optimal performance. PC's? They suggest replacing every 6mos to year. Halides? 9mos to year to keep optimal efficiency. These figures assuming your keeping all of the above cool with a fan.
In fact you can expect more light in your tank compared to a MH just for the fact the intensity is spread evenly throughout the tank giving you more options in placement compared to point source which gives you a 2'X2' coverage area via MH respectively.
In studies on tanks 24" and under T5 has shown higher readings than your typical PFO style MH. Some instances over twice the PAR of a MH.
-Justin