$ perl -MBench -e'$s = "a b"; /(\w+) (\w+)/; bench sub {$a=$1; $b=$2}, -1'
3666664 calls (3339959/s), 1.098s (0.0003ms/call)

$ perl -MBench -e'$s = "a b"; /(?<a>\w+) (?<a>\w+)/; bench sub {$a=$+{a}; $b=$+{b}}, -1'
636364 calls (560973/s), 1.134s (0.0018ms/call)

$ perl -MBench -e'$s = "a b"; /(?<a>\w+) (?<a>\w+)/; %h=(a=>$+{a}, b=>$+{b}); bench sub {$a=$h{a}; $b=$h{b}}, -1'
3333331 calls (3102372/s), 1.074s (0.0003ms/call)