Emissions question
 

Will a WRX with only one high-flow cat in the downpipe pass CA emissions? Those with the Perrin downpipes with the cat, have you passed? Thanks!

any modified part will technically not pass the visual inspection we have here in CA, even if it passes the sniffer test...

unless you have some really cool smog guys checking your car (yeah right)

Nope, no passing for you unless you get hooked up on the visual. Even then, unless your remaining cat was replaced also and is a 3-way, you will probably fail the sniffer test. Getting a single high-flow cat may allow you to pass the analysis.

most people are just going to put the stock dp and midpipe back on, hopefully we will all pass without having to put our uppipes back on.

Each catalytic converter uses a different coating to create a different chemical reaction with certain exhaust gases, and the toalt effect is cleaner emissions. Removing one cat could cause one or more of your pollutant levels to rise. It's actually almost 100% that they will- but whether or not they rise enough to fail you is a function of the efficiency of your particular individual engine.