Popped it in the benchmark, just for fun. Suffers from Out of memory! at large strings (like RobertCraven's original), but fastest of the full string comparisons:

     20000 26 20
               Rate         hdb RobertCraven   sortPosns    kennethk  
+       xxx
hdb          2.73/s          --         -15%        -41%        -55%  
+      -84%
RobertCraven 3.20/s         17%           --        -31%        -48%  
+      -81%
sortPosns    4.61/s         69%          44%          --        -24%  
+      -73%
kennethk     6.11/s        124%          91%         32%          --  
+      -64%
xxx          17.1/s        527%         435%        271%        180%  
+        --

     20000  4 20
               Rate         hdb RobertCraven   sortPosns         xxx  
+  kennethk
hdb          2.95/s          --         -10%        -36%        -43%  
+      -52%
RobertCraven 3.29/s         11%           --        -29%        -36%  
+      -46%
sortPosns    4.63/s         57%          41%          --        -10%  
+      -25%
xxx          5.15/s         74%          57%         11%          --  
+      -16%
kennethk     6.13/s        108%          87%         33%         19%  
+        --
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