I think that, if you are intimately familiar with a piece of kit, small changes will be more exaggerated than to the less familiar listener. To be honest, as a non-Yamaha user, the differences between the T3 and T4 are FAR subtler, from what I have heard so far (including Yamaha's demos) than Ian perceives.

Now, that is NOT to say they aren't there, just that you need a fair amount of familiarity just to hear them.

I can hear differences between E80 and G70 renditions fairly well. I doubt many non-Roland users could, though. To a Korg user, to a Yamaha user, a Roland is a Roland is a Roland...

To a non-Korg user, I expect the same problems. Differences are subtle. I am reserving my final opinion on this arranger until Korg officially release it, then, being Korg and not Yamaha (!) I would expect maybe two or three years FURTHER refinement as OS upgrades and sound tweaks get released. Korg's don't get released set in stone like Yamaha's do. DNC itself was an update to an arranger that didn't have it. Sure didn't see anything LIKE that from Yamaha.

And Korg's voice editing is down to the sample itself. So, unlike some other arrangers, if the sound doesn't QUITE suit you, at least you have the opportunity to correct it, or load in someone else's edited voice.

Once your sounds and styles are in RAM rather than ROM, a lot of the rules change...

But, for anyone without a Korg right now, just as with every other arranger manufacturer (what WAS the last arranger that was a RADICAL departure from the previous model?), don't be surprised that you can't hear MUCH difference. Few of us can hear it in YOURS, either...
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An arranger is just a tool. What matters is what you build with it..!