Slow performance accessing Ubuntu Samba folders
You should avoid using SMB on OS X (IMHO) as it has been buggy since the days of Snow Leopard (10.6), for me at least.

A quick Google search limited to this year alone brings up a myriad of issues regarding OS X and slow SMB implementations. 

There are a few  things you can try:


Use the SMB2 protocol by mounting your share  cifs://&lt;whatever your share name is&gt;
Enable AFP (Netatalk) on your Ubuntu server and connect to the mount points using afp://&lt;whatever your share name is&gt; 
Setup NFS on Ubuntu  and mount them on OS X 


Personally, if I have found CIFS good, AFP better, and NFS (even though it's much older) to be the best in terms of performance.