'Single-speed' drives are now obsolete and have been replaced by drives advertised as double, quad, six, eight or ten-speed. Even double speed drives are rapidly disappearing so quad and six-speed drives are currently the norm. They offer the best ratio between price and performance, with faster drives attracting a price premium.
It's worth noting that there are differences between drives operating at the same overall speeds, so some makes of drive may perform better than others of the same speed from different manufacturers.
