I'll go through this again for those who haven't heard my shpeal on high flow cats. So all the factory cats on the WRX are honeycomb design. So are the cats on the Turbo XS and most other downpipes out of the US and Australia. They are cheap (about $100 retail) and are available in larger sizes which allow them to flow more than the stock unit due to increased diameter. Now, the core itself doesn't actually flow any more per square inch then your stock one so "high flow" is kind of misleading. It's simply larger. Now there IS a cat that does outflow the old style honeycomb cats. That is a metal cat. Metal cats use a metral subtrate as a core thus eliminating the honeycomb restriction and allowing a straight shot through the cat core itself. it also cleans the air very well and can handle larger amounts of heat without breaking apart like a standard cat. The cores are all manufactured by a company out of Germany called emitec and are then sold to one company in Japan that I know of (Metalit) and to many auto manufacturers as well. Ferrari, Porsche, BMW, Mercedes, even Honda (in the S2000) use metal cats to improve performance while meeting emmission standards. Problem? They are very expensive. Since Emitec's US office is down the road from me I experimented with these cat cores years ago but found the cost prohibitively expensive to achieve what I wanted to do with them. Just was not worth it. Now, Japanese manufacturers DO offer metal cats. Cusco and Zero Sports offer downpipes for the WRX complete with metal cat cores in them. They each cost about $1000. Apexi also just released their metal cats for the GTR and the EVO. They are also quite expensive at around $700 retail. Again, it just depends on what you want to do.

Is there more power from running no cats? Yes, absolutely. How much more? I'd say 5-30 on the WRX. Just depends on what mods you're running.