Bad cat turns car into dog?

[01I30Beater]

Ahoy there fellow Infiniti folk. I'm hoping to get a little advice regarding a potentially big problem. I have a 2001 I30, with 103,000 miles on it. I paid $6000 for it a few months ago, at 96k miles, then put about $900 into it. I went to the only local Infiniti dealer to have them thoroughly go over the car and do an extensive servicing; new plugs, oil change, tires rotated/balance, induction system flushed, tranny/radiator fluids changed. All that cost 600 after tax, then later, I paid 300 to have a new MAF sensor put in, as it caused the car to run very lean and the SES light to come on.
So now I have a bit of money into the car, and I have to get it inspected within the next 3 months. Sure enough, the SES light has returned, this time giving back the code P0430 - rear catalytic converter fail. I work at a Nissan dealer, who cleared the code. Their advice:
-Hopefully it will stay off long enough to pass emissions inspections
-Just drive with the light on, you could go another 2 years, no problem
The light was off, and I went over 1,000 miles with no light on. But last night, while merging onto the highway, I pretty much gave it full throttle. I never do that, but for the heck of it, I wanted to hear the V6 snarl and see how fast it could go. About 2 minutes after that, the SES light came back on. Damn it - 2 more weeks and I could have passed emissions.
Anyways, I'm not sure what to do next. Disconnect the battery, and hopefully the code will go away? Replace the rear cat? Will the excess backpressure cause the engine to fail... if so, how long do I have? I would greatly appreciate any input on the matter, also an idea as to what a fair price would be to have this done. The dealership says the part is $600, plus labor. A decent indpendent guy qouted 350 for the part, 550 out the door. Slick Willy around the corner will install whatever I bring him for $50-100 in labor, and I found a $113 rear cat at this website:
http://www.car-stuff.com/carparts/infinitii3020002001easterneast400751.html

[spock]

If it's verified to be the cat at fault and not a bad sensor, then I personally, would do the Eastern cat and get Silly Willy to install it.

[01I30Beater]

That's Slick Willy, not Silly. The dealer told me that those crappy $100 converters are garbage, that I'll just keep getting the SES light on and that you get what you pay for. I'm thinking the midde-of-the-road option might be best - 500 bucks and I get it installed at a place of business that will stand by the work, not just do it for beer money.

[spock]

PO430 is actually Bank 2 cat.

[01I30Beater]

Well I found a solution - I disconnected the battery for 7 hours. I returned to fire it up, and glory hallelulah, the car started right up and there's no SES light on anymore. I've gone about 50 miles on it so far, and the light hasn't come back on.

My idea - On Dec. 1st, I plan on taking it the dealer for a state emissions and inspection. I need the light to stay off, and I'm guessing driving really slow will help. I think the light came back on because I accelerated pretty hard getting on the highway a few days ago. I also accelerate mildly, but that one day, I wanted see what she could do, and floored it. So my logic - heavy throttle = lots more exhaust being through. I think it resulted in enough extra pressure to trip that check engine light, warning me of a bad catalytic converter.

So... I'll just keep my RPMs low, crawling around, never accelerating hard.. and I'll be ok, right?

[spock]

Fill 'er up with premium fuel as well.

[01I30Beater]

Pfft - It took me one week to realize premium is ENTIRELY NECESSARY. I bought this car in May of 2009... figured, eh, it's the beater, I'll use the midgrade 87 oct stuff and be fine. NOT - Whenever I accelerated, it sounded like rocks tumbling in a jar, like a crappy Domestic car. I assume that was what people refer to as 'pinging', 'knocking,' and 'pre detonation.' Didn't take me long to switch to premium, and now I hear nothing but a polite, dignified hum.

[spock]

Really? I just suggested premium to get you through the etest. I bought mine in June 09 and for the first 3-4 fills used 87. I had no problem with knock/ping. I have been using 89 for the past 3-4 mos just because of reading of issues with the cat(s), etc. Don't really notice much difference between 87 & 89 performance wise.

[01I30Beater]

Yep, really. The car sounded horrible running the mid-grade 89 octane. That was before I went through the 100k mile tune up, so perhaps that would have smoothed it out. But I'm still sticking with the 93 octane stuff - hopefully it will keep my cat clean enough, boost the mileage a bit, and overall keep the engine running best. So you actually run 87 octane? The cheapest gas out there, and your car runs just fine? Maybe they tinkered with the engine when the blew it out to 3.5 litres, and they burn cheapie gas better than the 3.0.

[spock]

The manual says that 87 is the lowest octane you can run, but premium is recommended for "best performance. It acutally says that inside the fuel door too. I figured I'd split the dif and go 89. Not too many stations even have 93 around here. Sunoco does, but @ around 12 cents a liter more than 89.