I stopped using 3Delight the day after Iray appeared, so I can't testify to any improvements there. But Iray seems much more stable to me, maybe even slightly quicker. It can handle significantly more figures in a scene (roughly 2or 3 in 4.8 to 7 or 8 in 4.9) and using Iray to preview in the viewport is much more responsive. In fact the whole program seems more stable. In 4.8, GenX2 would usually crash when loading a figure into it for the first time, that doesn't happen with 4.9. Another advantage is that the database is significantly quicker when showing content, Even massive directories take only a second instead of several.

It's also worth bearing in mind, as there is a lot of confusion and mis-information about this, but you don't have to use Daz Connect or even see it. You can carry on with DIM or manual installs just like with 4.8. There is no need to sign in or send them any details. It will all work perfectly well in offline mode and that's what I'm using.