I can't find 'Small send buffer' option in the newest version of DC++

As of version 0.68 this setting is removed from DC++. Now you can fine tune the size of the Socket Write Buffer in Experts Only panel of DC++ settings instead. The setting defaults to 8 KiB and you can try to change it to a smaller value if you want to get the same effect as with 'Small send buffer' option before. You should specify the value in bytes and you may have to try several values to test what size suits your connection best. Note that you should restart DC++ to changes take effect.
Read more : http://dcpp.wordpress.com/2007/09/17/sockets-and-buffers/