Need your speedlight to recycle real fast? My first and foremost suggestion would be to shoot in manual mode and dial down the power setting. However, if I absolutely needed a power pack in order reload my speedlights in 1 second after a full power pop, then I would have a look at the Godox ProPac PB960: http://goo.gl/bD1B0G

Photo: Melinda in her favorite bikini

Watch the BTS video in Good Light! Magazine Issue 09: http://www.GoodLightMag.com/editions