Had a first taste of 10-abreast on one of the regional 773z. At the first Y bulkheads, legroom ok even at the window (6'3). But the seats are very narrow indeed. My other shoulder was occupying a good part of the middle seats airspace (luckily empty for most of the flight). The IFE control dock also sticks out from the arm rest, reducing the width even further. I find the seats more comfortable than other variants, very similar to the A350s, but YMMV.
Overall, the seats and the config seem fine for shorter regional hops (up to 2.5 hours), but wouldn't like to sit a LH flight on one of these...