Instead, it can stress out your legs. And using all legs to go faster doesn't work because bicycling is essentially an aerobic activity. Strong heart and lungs are the key. Therefore, to increase speed, work up to a cadence at which you feel steady and comfortable for long periods of time. A higher cadence in any gear equals greater speed.
Many factors play a role in determining which gear to use.
We have already explained why desired speed is not a consideration. Now let's see what is important to gear selection. The two or three sprockets in front are connected to the bike's pedals. From five to nine sprockets abut the real wheel. Choosing a gear boils down to deciding which two sprockets the chain belongs on at any one time.