The TRD's hp gain is very similar to TOM's barrel. Also, the tip of TRD is very similar to our stock tip. My friend tell me he did not feel any big difference in HKS an TRD. But he said may be the sound made him feel HKS is better hp. No dyno prove don't know. In my opinion, you can't compare the Altezza (rumble engine sound)to our IS300 (slient engine sound), if you put a TRD exhaust on your IS300 can't notice much difference in sound and also looking than stock.