gsr. dispite the itr's higher compression, they dont make as much power boosted. the itr cams are too agressive, and thats really bad on a boosted motor for 2 reasons. depending on the turbo of choice, you either have too much backpressure in the manifold (small turbo) at high rpms, so the extremely hot exhaust gases are forced back into the cylinder (called reversion) which superheats the combustion chamber and causes detonation. if you have a big turbo, the large overlap of the itr cams cause boost pressure to leak out the open exhaust valve, which is obviously bad for power. the itr's compression is also so high that you get in a viscious cycle with the timing. you need to retard the timing with boost regardless, (that reduced detonation, but it also causes heat). you have to retard the timing so much in a boosted itr that you begin to heat the combustion chamber enough to cause the detonation you are trying to prevent.
a gsr, while still a high compression motor, is less than the itr, has cams far more suited to boost (gsr cams have been used on drag cars making upwards of 500 whp) and you can make the same, if not more power on a gsr than an itr, with a motor that costs far less than an itr, and is far more likely to live driven hard on pump gas than an itr. you can run the gsr quite a bit leaner than the itr, again, helping power. even if they cost the same id still pick a gsr over an itr any day of the week.
and ur article supports what im saying 100%...so u mite wana do some reading urself