The cost per lumen difference between T8s and T5 HOs is pretty small, based on numbers I've seen. The bulbs are also harder to find and more expensive. I was considering upgrading to T5s but at this point it doesn't seem worth it to me. T8s may eventually get phased out, but I feel like that won't become an issue for several years yet. I don't really understand the argument that T8s are hilariously obsolete. It's nothing like T12s.