200 is a pretty standard chase. All they need to do is score at about 5 an over for 23 overs and then play the rest like it is overs 40-50. In fact, if they go like they have been, they could easily be up for a chase of 230. At least with 200 or more, if England get bogged down, they may feel the pressure. 180ish won't cut it, because they'll be able to just close in on the target safely.