Changing 100000 to -3 (means 3 seconds) and changin timethese to cmpthese gives:

             Rate defined  exists   as is
defined 1961549/s      --    -10%    -12%
exists  2181802/s     11%      --     -2%
as is   2236990/s     14%      3%      --
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Oddly enough, defined is slower. Then again, this isn't a very accurate test since the condition always evaluates to true. Also, any time loss is so minute compared losses from other inefficiencies that it doesn't matter. Deciding which of these to use based on efficiency is like trying to trying to what kind of gum to buy based on how long it takes to remove the packaging.