I acutally run a 46 / 16, but yeah, at 27 i'm just at the limit of feeling in control. I can make 30mph downhill but only if I can see the road is empty. I always think speed on climbs is more important :)
Poor form. I am fat and old but can manage 40mph on 48/19 - manage is a stretch - more like just about endure the feeling my legs are about to be ripped apart at each joint.
spin out? at 124 rpm cadence? you need to work on your pedalling.