Well LD1 as you stated, it's only like 1,000 or less yards mainly due to the deepest point being a very small area. To go that deep, you're mostly working around from edges going down hill toward the center. One section is about 3-4 feet deep for a about 1/4 of the pond area too.
FTG will possibly have a hard time going 6' deep in that small an area unless entering and exiting in same direction and can expect a steep incline.
I can assure you, however, that the bulk of the work was indeed done in 2 days and really started on a whim after reading so much about others' ponds. I had a natural run-off area to begin with where I get all the neighborhood's run-off directed through my property. After a couple years of mowing an ever moving ditch-line, I decided it would be a great place for a pond with the amount of watershed it gets. So I started digging.
Main reason I didn't use the Box Blade much is that I didn't need to. The FEL with tooth bar digs well and it is obviously more efficient to only handle each load once instead of running back and forth ripping, then scooping.
Also LD1, you mention spoil pile 100' from the pond. I put mine less than 10' from the top of my pond (actually started like 25' away, but kept moving back toward the pond as it grew). Then, my neighbor asked if he could have the spoils so when I got done, he brought is dad's skid steer over and moved the pile himself to his property. Now if I had had to relocate all that, then your argument and reasoning would make sense, but I did not count that time in my digging time. My 16 hours was mainly getting the bulk of it dug (including the core trench) as I mentioned. Along with that, I built the dam and packed it in layers as I dug, so about 1/3 of the spoils went into building the dam. Fine shaping and smoothing work was done later and in a little time here and there that as I stated earlier, I didn't count or include in this. Also, I do have red clay, which I would consider somewhat hard ground, but a tooth bar makes a ton of difference and I had no problem getting heaping scoops. The hardest part is maneuvering in and out of a bowl with a full scoop. I almost rolled the tractor twice, but dropped the bucket quickly. The Box Blade and loaded rear wheels allow for very heavy scoops.
Also, when I first dug it, I left a small island with a tree growing up in it. Later, I came back and removed the tree and dug that area back out as well. I read about root rot so just took it out.
I'm merely giving my experience. Your L3400 would do the same with the same set-up.
