I know this isn't from an ITR, but results should be similar.

Motor: B18C1 - 2000 Integra GS-R, each pull below is with the stock crush-bent gs-r exhaust.
Mods for the red line: AEM CAI, 18 degrees base ignition timing
Mods for the blue line: AEM CAI, 18 degrees base ignition timing, JDM ITR 4-1 header and 2.5" carsound high flow cat



So having the header match the cat-back is needed? No. Don't think so.

The car hit nearly 170whp after removal of ps, 2.5" exhaust and vafc tuning. To break that down, it hit (same day) 163whp/120ftlbs with just the removal of PS, then a whopping 165/120 with the ps removed and the 2.5" catback, then went to 169.x/122.x with vafc tuning. As for the power under the curve, it was worse with the 2.5" exhaust until a good bit of tuning. The car was a bit slower with the 2.5" exhaust added (until it was tuned, changing vtec xover removed the biggest dip in power and the car was running lean at the high end so it gained top and low end, nothing between 5 and 6.5k though).