Which high flow cat (HFC) is best?
 

The two best 63.5mm HFCs in the $200 range seem to be Berk and EVS tuning. Is there any reason to pick one over the other outside of cost? Any others worth looking at?

Obviously the gernpipe is better but 4x the cost...

Buy the Berk HFC. Made in USA. EVS made overseas. Support US manufacturers that are making quality stuff when you have the option.

I don't think there's any scientific testing of these to determine what's "best." Few if any notes here regarding failures. Not sure what cat needs a CEL fix if it's working properly.

Anyway, no problems with my 63.5mm Berk high flow cat with roughly 20K miles on it so far.

-- Chuck

An OEM Cat does not require a CEL fix since the O2 sensor is detecting the mix the ECU is expecting. Most HFC's (Berk included) and test pipes include a CEL fix to prevent the O2 sensor from detecting the modified flow mixture from the additional uncatalyzed gases making it past the HFC. The drive-by-wire 06-09 S2000's are more temperamental regarding this issue. I think your sweet Gernby tune disables the the sensor input from the secondary O2 sensor so you don't event have to worry about it. I know Greg has his plate full but I'm hoping I'm able to get a tune from him as well.

This^

A cell fix is nothing more than a simple spacer for the o2 sensor, to keep it farther out of the exhaust flow. This can be a screw in spacer, or it can just be a longer o2 bung built into the design. This longer bung is what products like Berk include.

Yes 70mm version would be the best match for your exhaust.
Outside dB is going to drop some but inside the cabin it will feel a lot worse from all the drone.

70mm HFC will drone worse than my 70mm test pipe? That's discouraging.

The Berk HFC have been known to fail on race or boosted S2000s. The Rockstar and EVS Tuning HFCs have been proven on these applications. I went with the EVS tuning HFC on both of my S2000's, because the material and build quality was better than Rockstar's. EVS Tuning HFC are made in Taiwan, but Evasive stands by their products and will probably price match the Berk one too. SARD and HKS(I think) make HFCs too, but they are in the $800 range.

A HFC causes more drone than a test pipe? That is the first time I heard that. A test pipe will give you a louder raspy exhaust and a lot more fume smell.