In the Sierra , I consider a small stream to be 4 to 30' accross...but when 30' across we are talking 6" to 12" deep...spring fed . or a low CFS ( under 400 ) freestone... Gus , if you fished , when growing up , you might remember the Clavey , ( off 108 ) or Beaver Creek off 4...A Stream , to me is the same width , with more water ( deeper ) and faster...
I use a 2 Wt as much as possible... graduating to a 4wt when I have to...The Fall , Hat , Hot , Owens etc