As the spring rate and clamp load of the clutch increases so does the release bearing load.

The release bearing used should be a high quality steel caged radius contact ball bearing.
The release mechanism should be arranged so that the bearing is free of the spring fingers when the clutch is fully engaged. 

The release travel should be limited to the figure given for each clutch in the application guide, by means of an external stop to avoid damage to the diaphragm spring.

Suitable release bearings are available from AP Racing:-

Standard release bearing. - (Outer race rotates)
High speed release bearing. - (Inner race rotates)
Standard release bearing. - (Outer race rotates, Ø40mm I/D)

Download Bearing Installation Drawing Here: CP3457-7CD