ダブルクオートとシングルクオートの速度差は(ほぼ)ない ref: http://qiita.com/cielavenir/items/3bbb4e483df8ba03de03

file0.txt

%q(x=5;puts "aaa #{x**3}")

file1.txt

irb> RubyVM::InstructionSequence.compile(%q(x=5;puts "aaa #{x**3}")).to_a
=> ["YARVInstructionSequence/SimpleDataFormat", 2, 0, 1, {:arg_size=>0, :local_size=>2, :stack_max=>4}, "<compiled>", "<compiled>", nil, 1, :top, [:x], 0, [], [1, [:trace, 1], [:putobject, 5], [:setlocal_OP__WC__0, 2], [:trace, 1], [:putself], [:putobject, "aaa "], [:getlocal_OP__WC__0, 2], [:putobject, 3], [:opt_send_simple, {:mid=>:**, :flag=>256, :orig_argc=>1, :blockptr=>nil}], [:tostring], [:concatstrings, 2], [:opt_send_simple, {:mid=>:puts, :flag=>264, :orig_argc=>1, :blockptr=>nil}], [:leave]]]

file2.txt

irb> RubyVM::InstructionSequence.compile(%q(x=5;puts 'aaa '+(x**3).to_s)).to_a
=> ["YARVInstructionSequence/SimpleDataFormat", 2, 0, 1, {:arg_size=>0, :local_size=>2, :stack_max=>4}, "<compiled>", "<compiled>", nil, 1, :top, [:x], 0, [], [1, [:trace, 1], [:putobject, 5], [:setlocal_OP__WC__0, 2], [:trace, 1], [:putself], [:putstring, "aaa "], [:trace, 1], [:getlocal_OP__WC__0, 2], [:putobject, 3], [:opt_send_simple, {:mid=>:**, :flag=>256, :orig_argc=>1, :blockptr=>nil}], [:opt_send_simple, {:mid=>:to_s, :flag=>256, :orig_argc=>0, :blockptr=>nil}], [:opt_plus, {:mid=>:+, :flag=>256, :orig_argc=>1, :blockptr=>nil}], [:opt_send_simple, {:mid=>:puts, :flag=>264, :orig_argc=>1, :blockptr=>nil}], [:leave]]]