just playing the devil's advocate here
a car needs a teardown anyway after a muddy race, I would much rather just replace the bearings with cheapies as opposed to cleaning/relubing/babying bearings that cost me a days wage. It's more time and cost efficient to use cheapies and replace them at any sign of wear/dirt.
After one lap outside any efficiency gained is lost by the addition of dirt, dust, bugs what have you. Unecessary fluff! Especially for a car driven in dirt.
Save them for the gold plated shelf queen!
that's just me though.........