Earlier quoted context omitted.
Gazelle does at least 5.5km/s.
But how long does it take to get to that speed?
Spent a very enlightening afternoon down an old bunker near pervomaisk.
Found some stats in the tourist brochure from there. 9.4m high,1.1m dia, 4km/s in 4s, which gives an acceleration if about 102g. 80-100km range. Max speed 7km/s. "directional blast" also, which is interesting.