Hey Joel,
I've been diving Blue Springs for 10 years, though I'm still a novice to some degree in the general freediving realm. I think I've been to around 80 feet or so but I don't dive too actively or aggressively. I can give you some general pointers for this dive.
Coincidentally, I'm also into video editing but not of freediving, check out some of my work in the gallery at
www.matthoover.com.
Anyway, from watching the subject in the videos I noticed two main things.
1. He's not wearing a wetsuit.
2. He's finning a lot to descend.
Get a wetsuit and a weightbelt. LEARN how to properly weight yourself, the rule of thumb I was told long ago is to be positively buoyant above 30', but I do not claim to be a freediving expert so do not take my words as advice.
Pull yourself down via the ledges rather than finning. You will expend less energy. Avoid the flow, which is explained in the next paragraph.
What you REALLY want to do, but this requires knowledge of the terrain down there, and a light (and another disclaimer that you do this at your own risk) is go down in the narrowest end of the crevice (there is a very narrow dark route not accessible from the surface, you may need to be shown) and completely avoid the flow - below your neutral buoyancy point you will sink. You will come out at about 50 feet on that long shelf above the sign, but way past the sign horiztonally, in the darker half of the cavern. From there you can go deeper, or simply turn back toward the sign, get back into the flow, and "ride" it to the surface as you fin.
Any deep dives beyond 60 feet require a lot of horizontal movement as well, so an 80 ft dive is not simply 60+20.
If you think it's cool swimming down to SCUBA divers and waving, wait until you see the confusion on their faces when you ascend past them at 50 ft, and they never saw you going down in the first place.
P.S. I really dig the Ratatat song, I have been hearing them on the local indie station and liking it, your video was the last straw, I am going to have to go get one of their albums.