Your quantum should be able to fly down to 5 mph. It will require adjusting the bridle to create more lift, and more (body) movement than you're used to (when wind is inadequate, we make our own). Also, flying a standard down to its lower limits, requires much more finesse or a lighter touch. Practicing with your quantum down to 5 mph will help you develop the skills to start doing slack line tricks, and make it much easier when you do finally acquire an UL or SUL.