For another $30 you are stepping up to a completely different class of machine. I have the G0513x2 and it is so much more ... hmm ... industrial ... beefy ... massive ... than my Jet 14". Just looking at verious specific parts, it's clear that they are completely different classes of machines.
The tensioning spring, for example. You could probably fit two of the Jet tension springs INSIDE the coil of the Grizzly spring and still have room. It's made from much thicker wire and is far larger than even the Cobra replacement spring I put on the Jet. It's a monster!
The wheel bearings. The Jet's wheel bearings, while sufficient, look measely compared to the massive bearings on the Grizzly's wheels. They just have that much more ruggedness to 'em.
The tension adjuster is another major difference, but I don't think it's an equal comparison since the mechanisms work completely differently.
I'm not sure how similar the G0555x is to the Jet 14", but they're certainly not miles and away different. Every 14" bandsaw I've seen has that same spring and wheel bearings. These two factors alone would be worth the extra $30.
I can't say I've ever run into the throat on my Jet 14" before, so the extra few inches of throat aren't all that valuable to me but they could be to someone.
My only gripe with the G0513x2 that I have is that changing blades requires an allen wrench whereas my Jet has all thumbscrews for adjusting the guides. Minor pain and something I will address soon enough anyway.
I think you'd be really missing out on an opportunity if you passed up the 513, personally.