Some info from K-Mac on strut tops -
The K-Mac Stage 1 kit for street use is steel with ball bearings and urethane, $380 pair inc GST
Stage 2 - Street/Race - all alloy with pillow ball bearing in urethane, $480 pair inc GST
Stage 3 - Full Race - as Stage 2, but no urethane/flex, $480 pair inc GST
Note that the centres are replaceable in Stage 2 and 3 kits, giving effective lifetime usage.
Cheers
Matt