You have to start with how far do you tow and how often? That's a pretty big ($$) jump to go to a triple Extreme trailer from the stock trailer. There's a lot of people who will say that Extreme is the better and has very good custmer service. And I have to agree, the Extreme is a better made trailer than my Zieman. Knock on wood, I haven't had any trailer problems so I can't tell you about Zieman's customer service. I only tow 12 miles each way to the launch ramp.
I have a triple axle Zieman under my 29' Magic and I don't look forward to having to buy 6 new tires when it's time. Sure, triple's might look cooler but it's just more maintenance, and more wear and tear on your tires.
If anything, I would say just upgrade to the Extreme double with the Goodyear tires. Don't let them put crappy no name tires on your trailer whatever you choose.