Have noted your comment about acquiring further ex-Citybus and Ulsterbus RE's and the question of top speed. In terms of performance those with 4-speed gearboxes (will be ex-Citybus) all will have a performance characteristic similar to your 2531, ie max. speed in regional of 40/42mph whilst those with 5-speed boxes (could originally be either Ulsterbus or Citybus) should be capable of 55/60mph or possibly even a little more in favourable conditions.

It mat be possible to set-up the pumps to produce 3/4mph more but in the case of the 4-speed models it is unlikely that much above 45mph can be achieved, at least not without rebuilding the gearboxes to change the final drive gearing.