What are you planning for plants? The 40B is a great size for working in, and can definitely have a lot of depth to the scape.
Yeah, it seems like a world of difference from my old tanks. 55 is just not good for planted tanks at all. I like the progress on your 40B by the way, it's looking really good. I especially like the variation in colors you've got.
As for plants, that's a good question. I'm not married to any one idea just yet. Definitely don't want an HC carpet, that just seems really played out. I do like the look of starougyne repens and maybe a small area of microswords. I'm quite fond of mosses but if I get a bitchin piece of wood I don't plan on covering it up.