Thanks, everyone!
I tried the same thing with a big billowy cumulus but the render time was just intolerable for me here. I may leave a small one running as I know it looks very nice from my tiny tests but it might take some time to render it out. If you're planning on doing a large billowy warp movement, values of '0.01' increments work very well for this.
I warped a large cloud from '0.25' to '0.275' over 250 frames and that was still a bit too much because you'll want the large features to have minimal movement while the smaller parts gently 'boil', too large values move the whole cloud too much so keep it really subtle for best effect. Using a secondary warp on the density fractal might give you more control of the warp amount but I prefer to use the density fractal's own warp settings, as it warps according to the actual shape of the fractal and not any secondary warp function.
I'll post back here if I manage to render out a decent cumulus warp sequence worth sharing.