If you want heat quick, think about a car radiator, as it is designed to dump heat as quickly as possible. Lots of thin metal and airflow to dissipate heat quickly.
The heat coming off the top of your stove has already been transferred to your garage. Like Douglas said, you need to capture more heat from the flue gasses to increase efficiency. I like Lisa's heat sink idea. They also made commercial heat exchangers that fit in a flue stack. Another simple method is figure out a way to lengthen your stove pipe inside. Beware that lengthening, slowing, and/or cooling flue gasses can result in creosote buildup and increased chimney fire risk. The solution to this is to split wood small and only burn it bone dry, being careful not to over fire your stove. Your wood should always be bone dry, as it takes a lot of energy (wasted heat) to dry out wet wood. Store your wood under cover, with good airflow, for at least a year, longer if possible.
For now, I'd focus on sealing and insulation. You'll see more improvement from that than you would a few percentage points in efficiency on your stove.