Ya sometimes the dyno graphs can be confusing because they were not all done at the same time. This is a good example of that. We did the catback results one day, (very repeatable), then the next did the front pipe stuff.
The other slightly confusuing thing is the numbers you see in the boxes, this just represents where the cursor is at on the software. You can see that we didn't compare the peak power on each run, but rather areas we thought were important.
What is boils down to is the variance in HP on the car. We have see this be a huge factor for showing dyno results on things. In fact I experienced this last weekend tuning. I was making 193 WHP on our NA car and the next day it was down about 10 HP. At least until the engine got about 20 pulls into the day and got fully warmed up. Oil temps are key to making power. HP is lost until the oil gets to about 80-90C, then then engine is good and happy. Then it seems to loose power as oil temps go above 105C. Here is a dyno graph showing the huge variance in HP as a car that is fully warmed up, goes through about 14 pulls on the dyno.
More info about why you want an oil cooler can be found here!
If you have more questions about this, let us know! Also check out the blog, there is a BRZ section that has more info as well.