Pass Labs X250.5 compared to X350.5?

Has anyone had a chance to do a side by side comparison between these two amplifiers and if so what were the sonic difference you heard?

I realize that the X350.5 is a more powerful amplifier. However, if one plans to use them with reasonably efficient speakers where 250W@8/500W@4 would be ample power, are there still substantial sonic gains associated with going with the X350.5 and if so what are they? The perception I got from reading this forum was that the X350.5 was the "sweet spot" in the Pass Labs X.5 lineup.

Your thoughts and experiences would be much appreciated. Thanks in advance.
I'm curious ,too, as I would love to listen to the X250.5 in my own system. From what I've read, the 350 stays in Class A to a much higher power level, as opposed to the 250.5, and I would guess that is what might make one prefer the more powerful of the two. I'm sure owners will give us both lots of good info.
Well I know that the 250 uses feedback and the 350 desent need it.