I can do the simple maths, not all this half GS stuff, but both are useful as a quick check.
As regards the STN airspace I am aware of that on 05 and often use speedbrakes to get down to where they want us, it was just the last little bit I was referring to.
Never thought of how big a difference the speeds make, maybe will have to go for Flap 2 to keep the exact speed (not that I ever didn't...)