Samba issues (deadlocks and instability) in OSX 10.10.1?
I've had similar problems compared to what you're describing, although it sounds like your problems are worse. It's very common based on what I've read and there's no cure. The issue is that Apple isn't using the Samba software but rather their own version. Here's my experience, FWIW:
SMB volumes were slower for me on Mavericks and older on these machines. Upgrading to 10.10.2 has sped it up and made everything work much better.
The shares are still very slow. One very large share performs much like you're describing at times. But other smaller ones are fairly managable, albeit frustrating.
We use Path Finder to connect to our shares, not Finder. This may be superstition on our part, as I don't know if it is actually doing anything different. But it does seem to give us fewer crashes.
DF in the terminal does not create the issue you have, it just lists like normal.
I have upgraded the RAM, but the hardware is older. One Mac Pro 2008 model has 8GB while another has 16GB. I've seen machines have a slow finder when they don't have enough RAM, but the problem is the software. Unfortunately, upgrading the RAM was the only solution I had to improve performance.
Windows shares may not list as slowly as my Linux NAS, but I have no benchmarks to prove that. (That would make sense if both weren't using Server Message Block.)
If none of this information helps you, may I ask if you've tried a fresh install?
As for me, I'm very interested in compiling Samba from source providing I can find enough support.