Units no longer have mandatory base sizes in 40K so you don't have to worry about being compliant. You can even keep the old square bases if you want.
If you want to upgrade for looks then the current plastic Wraithlord and War Walkers are both on 60mm circular bases. My metal Wraithlords are still on 40mm bases though and it does not cause a problem.
Sanguinius stood up, stretching his wings to their full extent. He flexed his hands. "I need no blade".
It was as though Sanguinius gleamed with pale light, his face white, eyes becoming blood-red, surrounded by the golden crown of flowing hair. Guilliman had witnessed glimpses of of his brother's wrath before, but had never seen the true Blood Angel unleashed. Sanguinius surged forward on alabaster wings, half a meter from the floor, whiteness streaming from him like flames.