Bearings could be a factor, but it's more likely the durometer of the wheels. That is, the hardness of the urethane determines how fast a wheel is. Harder wheels are faster, but less sticky. Another factor could be precision in machining. If the tolerances on the Grit are more accurate, then everything will fit better and there will be less resistance to smooth rolling. If the fork and wheel hubs are poorly machined, then it can impact how freely the bearings can spin.