D'Arcey, these are all available option for sfDropdown:
{ "Attribute" ,"attr" }
{ "Code Name" ,"codename" }
{ "Column Span" ,"colspan" }
{ "Default" ,"default" }
{ "Factory" ,"factory" }
{ "Caption" ,"hdr" }
{ "Lookup" ,"lookup" }
{ "No Empty" ,"Noempty" }
{ "OP Code" ,"op" }
{ "Window" ,"win" }
from here you can see that there is parameter for width.