The makers of HL2 predict about 30% performance increase on the version of HL2 for A64 compared to the 32bit version...
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Will Half-Life 2 have any special optimizations for 64-bit processors?
Gabe Newell: I would expect we would run about 30% faster clock for clock comparing an Athlon running 32-bit code and an Athlon 64 running 64-bit code. Release of the 64-bit client will be gated on MS releasing 64-bit Windows.
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