Smoke I have a few t8 fixtures and one t5 fixture now in my setup. And from my experience there isn't a huge difference in light output. The biggest differences between the 2 to me are: t5's are smaller (take up alot less room) and put out the same amount or a little more light than the t8 bulb to bulb. The t5's also cost a bit more for fixtures and bulbs.
T8's: for grows on a budget there fairly cheap, easy to construct from scratch too. They put out good light for vegging plants, they take up a little more space than a t5 hince there bigger bulbs, slightly bigger fixtures too.
As far as electricity used to lumens produced between the 2 I've never really looked into it.
I went with t8's over t5's mostly for my grow because there cheaper, easier to find and get parts for in my area. And there plenty for my space, I wouldn even own the t5 if I hadn of ran up on it as cheap as I did. My t8's in my flower space put out little to no heat also, I've had plants set there leaves right on the bulbs for hours and not burn the tips @ all. Not running as hot helps out alot when it comes to venting the space. Alright im done rambling, I hope this helps. Looks like your girls are doin great, you have learned almost enough that either route you go with lights you should be fine. That clone is looking good, she will be back to growing like a weed before you know it smoke. Happy growing...