Upgrade from 220pro CI to 250pro CI or 440pro CI

[Drifter]

I went from 120 -> 220 -> 440.
The jump from 120 to 220 was significant from a sound quality perspective but the 220 to 440 jump brought me the most pleasure. It added an effortlessness to the sound and certainly solidified the bass and widened the soundstage.
I've never heard a 250PRO, just the original d-premier on a few occasions both as a single unit and dual mono config.

Funny, the jump from 220 to 440 on my Martin Logan Summits was less significant than a speaker cable upgrade costing half the amount. The joy an upgrade from 220 to 440 gives seems to be highly speaker dependent.

It might very well be highly speaker dependent.
I've listened to a few Martin Logans. Since the bass drivers are internally powered the extra power from the Devialet mono config won't affect bass performance. I'm also not sure how the high/mid electrostatic panels reacts to more power.