(Clara BW is at 1% light since the Voyage is always lit at like half a percent, and I put the same fonts on both.)
If I didn't have them side by side I'd be impressed with the quality of the Clara's screen, but the Voyage has a slight advantage. Definitely better than the Oasis & Paperwhites. I only kinda miss the page turn buttons; I've been using a clicker for a few months now so it's not as big a deal. The official Voyage case has a better fold angle & front protection than Kobo's official folding one, and I'll probably pick up a third-party case at some point to hopefully solve that. They are nearly the same size, but the Kobo is much lighter: Voyage is 308g, and the Clara BW is 285g, both in their cases. The Voyage feels like a premium device, with its glass front and rubber edge. The Clara BW does not, but without a Voyage next to it it fares better.
Software: Clara BW is so much faster that I don't really care what the UI is like; it's actually usable. I do plan to install some tweaks for a few quality of life items I'd like to adjust (like getting rid of the huge bottom margin), eventually.
My Voyage is losing 5% battery every ten minutes and takes a different cable than all my other devices, so it's time to retire, perhaps. It'll always hold a special place with me, as a faithful companion for the last 10 years.