I've also been on a mission to find Dempsey St. I'm sure Mongibello is correct as the layout of the streets in that area then and now point to something destructive occurring (eg fewer streets and inexplicable dead ends).
I have also located it both on Cross's 1861 map and Booth Poverty Map where it is classed as "pink" - "fairly comfortable, good ordinary earnings"
Its in the map I linked to earlier, runnign north south and the link you posted to the discussion also backs my proposal of where it would be in modern day. The Wikipedia link to Stepney below states that Stepney was a poor area and was pretty much destroyed in WW2 - hence it being quite different in modern day
http://en.wikipedia.org/wiki/StepneyQuote :
The area was rapidly built up in the 19th century, mainly to accommodate immigrant workers and displaced London poor, and developed a reputation for poverty, overcrowding, violence and political dissent.[1] It was severely damaged during the Blitz, with over a third of housing totally destroyed, and then 1960s slum clearance and development replaced most residential streets with tower blocks and modern housing estates, though some Georgian architecture and Victorian era terraced housing survive in patches, such as Arbour Square, the eastern side of Stepney Green and the streets around Matlock Street.[
