I read your topic and was wondering what happened... I am glad it worked out for you.
Last night I exchanged the new T5 for an old T8. Side by side, the T5 looks much brighter, with a bluish white (10000K) which offsets the yellow of my old 5000K Octrons very nicely. They also create some nice bluish reflections on the Pearl Gouramies and Rams. Not sure how "good" they are for plants... probably some reds missing.
In it's own raingutter the difference wasn't that notable, because my reflectors (raingutter lined with mylar) were perfect for the T8's, which I put snug to the back of the gutter. I need a different angle for the T5's, which are a little bit lower because having their own fixture.
They do get quite a bit warmer than the (NO) T8's, about in between the T8's and the AHS 13W bulbs, about the same as the 10W PC bulbs from Walmart.
I like them, considering that they are "only" 38 Watt but a bit brighter than the T8. I do need to adjust the reflector though, but that shouldn't be too hard, since they are physically smaller than the T8s.
I will probably buy another one of those fixtures, to end up with 2 T5s and 2 T8s for now. If I could get the bulbs as cheap as you, I would convert them all... I suppose they would work with the 4x T8 ballast as well, using two outputs of each ballast for each bulb. Hmmm... I might end up with a high light tank after all :roll: