The existing runway movement rate is set by the capacity of departures on runway 08 as more aircraft need to backtrack using that runway and the backtrack is longer than for 26.
This is set at 34 movements per hour and will increase ultimately to 40 movements per hour as once the 08 end is finished the weak link then switches to 26 until that runway gets its new taxiway. I don't know what the interim movement rate will be apart from somewhere between the 2 figures but the 26 taxiway extension is only a small one in comparison to 08 so I would expect the figure will be greater than half the difference.
Another advantage to the 08 taxiway extension is that the junction to the main apron won't get blocked any more.
The exit route of the dual carriageway did indeed open as 2 lanes today for its full length and the inbound carriageway opened as 2 lanes from just past the traffic lights.
I would think this has more to do with commitments made to the airport about its opening date as there is still work to be done to the central reservation either side of the tunnel so the cones will be back out soon so the work can be finished. Also the traffic lights have yet to be switched on.