What does the two-core CPU get you? I'm very satisfied with my BW with KOReader, haven't noticed any shortcomings but I only read books on it.
I do like my BW kobo, but it's on the slow side, even just when switching pages on the stock app ; and that's annoying. Sometimes because it's stuck it doesn't register the page change, and then it will highlight text instead. That's breaking the reading flow and I really hate that.
I encounter freezes mostly when I enable Bluetooth/wifi. Haven't tried on a multi-core kobo but I imagine the UI thread can keep running there.
When reading, agree on it being more than sufficient.
My recommendation is partially because the price can be identical when they have a sale. That was the case when I got a BW--it was the same price as the color.
I should also mention I run quite a few things on my kobo: boringtun to connect to my home network, a fetcher to sync my books and feeds, Plato and its article fetcher whenever I update my Wallabag articles. I'm beyond pleased with my reader experience. The extra processing power would just be icing on the cake.