I would have to disagree. There was a recent test done by SMSP. He builds and sells a 2.5" catback exhaust with a straight through muffler and it only gained 3 HP over the Type-R catback exhaust. The test was done on a stock Integra Type-R. Here is a link to the thread: http://www.honda-tech.com/zerothread?id=332226I . So, there isn't really much to gain by going from 2.25" --> 2.5".

I have the Type-R catback exhaust on my '94 GS-R and it is a really nice upgrade. The fit and finish is excellent and the exhaust is only slightly louder than stock. Also, there is a very noticeable improvement in performance. The car pulls much harder from about 5,500 RPM and the engine is more responsive.