It stands to reason the AD/DA's are improved as are the effects on the T5, hence the differences between the T4/T5 albeit not significant.

I'd like to hear the sounds utilizing no effects or EQ side by side. I doubt they'll differ very much. Many keyboards rely heavily upon the internal FX and once you shut them off, the sound can be abysmal. The keyboards that can hold their own with no FX are relatively few.

I wonder if Yamaha is still utilizing mono samples, copying them, panning them in the stereo spectrum, and classifying them as stereo. They did this with many of their synths and arrangers and it always ticked me off. Not to mention it cuts polyphony in half.