Hmmm, I haven’t tried them side-by-side, but I think they are similar, or perhaps the white chocolate bc is a little more of a balance between white chocolate and lemon. But I’ve only made the golden dream wedding cake version, which is lighter and doesn’t use lemon curd (Woody’s lemon layer cake version uses the lemon curd).
The thing that I remember most isn’t so much if one is more lemony than the other- it’s easy enough to add lemon oil drop by drop to intensify either buttercream- it’s more that the white chocolate buttercream base in RHC doesn’t taste as buttery as mousseline. I think I may actually like it better, which is saying something because lemon curd mousseline is pretty darn tasty. 
