Indicated 150mph when I ran out of bottle (and road).
Probably 145mph in real terms.
Didn't take too long to get there, and felt good for another 5mph or so which makes the manufacturer quoted 149mph seem about right.
The road I was on was a hilly, twisty stretch of dual carraigeway, which made the feat even more impressive. Car felt pretty stable, considering it is essentially a family hatch on morphine.