Currently, in PhaseCFG::hoist_to_cheaper_block(), StressGCM follows the GCM heuristic when the candidate block has strictly better frequency and only only randomizes tie-breaking among equally frequent blocks:

if (LCA_freq < least_freq              || // Better Frequency
    (StressGCM && C->randomized_select(cand_cnt)) || // Should be randomly accepted in stress mode
    ... 

The randomization scope can be significantly extended by allowing GCM to move instructions to blocks with worse frequency at random:

if ((StressGCM && C->randomized_select(cand_cnt)) || // Should be randomly accepted in stress mode
    (!StressGCM && LCA_freq < least_freq) || // Better Frequency
    ...   

This would improve StressGCM's ability to expose bugs where C2 relies on GCM heuristics for correctness.