Well a high flow cat sounds like a good upgrade, especially considering the cost of it.
I'd go for it, a good investment too. As mentioned in the TechInfo, willwren'* topic shows that once you have a 180 thermostat and have the car breathing better with a custom intake (even a gutted airbox), that the next step is usually a high-flow cat and / or muffler.
Here'* the topic, I think it helps give a nice overview too. Didn't know if anyone'* posted it yet... lol.