Zen Tenkara rods are high performance, strong rods. But exerience and skill still impact the various successes you can have on different tippet sizes. This is a general rule of thumb:
Hachi Tenkara rod: 7x, 6x, 5x, (once expereinced and familiar with rod flex profile 4x)
Suzume Tenkara rod: 7x, 6x, 5x, 4x
Zako Tenkara rod: 7x 6x, 5x, 4x (once expereinced and familiar with rod flex profile 3x)
Sagi Tenkara rod: 6x, 5x, 4x, 3x, (once expereinced and familiar with rod flex profile 2x-12lb)
Sumenkia Tenkara rod: 6x 5x, 4x, 3x, 2x, (once expereinced and familiar with rod flex profile 1x)
Taka Tenkara rod: 6x, 5x, 4x, 3x, 2x, 1x, (once expereinced and familiar with rod flex profile 0x)
Kyojin II Tenkara rod: 3x, 2x, 1x, 0x, 16lb (once expereinced and very familiar with rod flex profile 20lb)