Good questions to ask for sure regarding LEDs run time, height, and ect.. it would be nice to have a base line as with MHs and T5s. The reason there is no base line with LEDs is because right now designer's and manufactures of the fixture we are using are using us Hobbiest to learn from. This is evident by the on going upgrades to their products with all the top company's......I have seen a lot of advancement with LEDs over the last two years but believe it will be some time yet before we have LED base lines.
What we do know is go slow with LEDs because each system is different and share what you have learned. As you can already see from the post's one hobbiest loves Kessils another doesn't, one hobbiest loves radions others don't. One claims radions have the highest par/pur I believe Orphek does so we are all still just learning
If we keep sharing what we know and not what we think we will someday have a LED baseline all can use.
Good luck with the information you seek