When in good order they were sprightly performers and running on third rail with the full brought to bear (the original class 71 traction equipment having been down-rated slightly from to extend service intervals), many runs in excess of were noted despite a stated maximum of - though nothing approaching this was achievable on diesel power. Their electronic power delivery meant that acceleration was equally impressive on both diesel and electric power sources. Running on the diesel engine however, available power was pretty much exhausted by the time or was reached with 'normal' loads and heavy loads (even eight or nine loaded milk tanks over the banks of the West London line) would tax them. Speeds would drop and recovery margins in timings taken full advantage of.