Eric Brown was touching down at 105mph.
Once he went to idle setting on the engine during the approach the pilot was committed. Idle gate was selected when the pilot was sure of not undershooting. Approach speed was 125mph. The engine would not respond in time (spool up) for a go round if the pilot overshot the runway.
According to Brown the brakes were better than typical German (which normally was bad) but not up to task of stopping the plane without a lot of runway.
BTW it took a full minute to pump the flaps down.
IS-2 made four test flights, but you are right - seems, that the maximum speed was not measured. I saw a value of 593 km/h for estimated top speed in one source, so I assumed 588 km/h were achieved in flight, but this has not been confirmed by more reliable sources. I apologize for the inaccurate information.
P.S. There are good reasons to believe, that the IS-2 was capable of reaching 570 km/h at least - if the engine was working reliably. Anyway, this sophisticated airplane was rather an archaism than a fruitful idea.
C'mon guys. Enough of those passe' losers. There is NO Contest!
The Scarlett Stormer was undefeated, flying against the best Axis aircraft, NEVER shot down, and capable of operating from land, sea or snow without special equipment!!