Boeing 720B performance
As previously mentioned the B720B was over-powered and actually capable of higher rates of climb than would ever be used with passengers on board. London ATC loved them - requests such as "Monarch 2344, can you make FL290 by Midhurst" would be answered by "we can make FL370 if you like".
I experienced an extreme example on 17/3/82 on G-AZKM. This aircraft was stripped of its seats for part of the winter and kept on standby for any ad-hoc cargo flights. On this occasion, the regular Air Bridge Merchantman, which took newspapers to Glasgow 6 nights a week, was unserviceable and 'KM was "scrambled", loaded with around 18 tonnes of newspapers and headed to Prestwick (GLA was closed for runway work). I was "persuaded" (very easily of course) to travel as loadmaster, which was a welcome relief from an otherwise boring winter night shift. Before the return sector, the skipper asked me if I was up for a bit of fun i.e. they were going to see how quickly the empty aircraft, lighter than usual with no seats, carpets or cabin crew, could reach their cruising level of FL330. Answer:- 4 minutes 30 seconds ! i.e. around 7000 fpm climb rate. Yes the ears did pop a bit. Just as well it was dark and I couldn't see the horizon at a 45 degree angle....