(time (fib-test))
    1750 collections
    18.410461000s elapsed cpu time, including 0.111755000s collecting
    18.502651000s elapsed real time, including 0.115357000s collecting
    43407534256 bytes allocated, including 43373090944 bytes reclaimed
    
(time (run 4 fib-test))
    1937 collections
    88.858037000s elapsed cpu time, including 0.416044000s collecting
    26.084823000s elapsed real time, including 0.421594000s collecting
    173718154128 bytes allocated, including 173714549616 bytes reclaimed
    
Chez Scheme's memory management is parallel. CPU usage ~370%.