Really when I did my research, I went with the conclusion of t5>led>mh. Really to replace a t5 on an established tank, you just won't get your money back. From how the led kits work, and look, they are a replacement for halides, not really t5. You will get plenty of growth from a 4-6 bulb array for about the total cost of a new led setup.
Now if were talking about a brand new setup, there seriusly is nothing better than led, if you can build a setup or want to...
8 bulb unit just isn't worth replacing imo