I used a pellet weighing 14.2 gr and got an average of 643 fps. That's about 13ft-lb of energy... It's still stock standard and probably will stay that way, at least for the foreseeable future. Super quiet with the addon attatchment. Very deceptive, as all you hear is the sound of timber being invaded by lead...
As an extra - I also chrony'd a Zoraki HP-01 (Webley Alecto) pistol and achieved about 570fps with 7.6gr .177's but what surprised me was the noise this pistol makes when fired. Quite an almost eardrum splitting bang...