I pulled a backup of the server world yesterday, and I just did a local test after pruning regions as indicated in 709's post (minus r.-6.0 per Elysium's post), and it looks like the biome blending is still really good!
I flew out to the border between r.-6,0 and r.-5,0 to see how it performed, and I am impressed. Preserved r.-5,0 on the right, deleted and newly generated r.-6,0 on the left. If not for the occasional blocks of snow (???) between them, I wouldn't have guessed where one started and the next began.