Cold air is better than hot air at the inlet no matter how good the IC is. Cold air is denser and your turbo will more more oxygen molecules with denser air. Not terribly significant but it is better.
The real problem with short rams is that the hot air throws off the ECU temp. corrections. The hot underhood air makes the ECU (which has temp. correction tables set up for cold air induction) think that it 1pm in Death Valley on the hottest day of the year, when really it's just a mild summer day. The ECU then pulls timing, and you can feel it. The temp. correction tables can be redone by the tuner but this is not done for any stage maps I know of. Also you never really know if the IC is heat soaked which is really what the ECU needs to know. Subaru should have an intake air temp sensor after the IC, because this is where it counts - just before the air goes in the engine... but it doesn't. This is one of the big advantages of blow-thru MAF - the IAT sensor is part of the MAF sensor and with BTM the temp. will be sensed after the IC.
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