Thanks for the reply
The reason I want it isn't because of speed (it is irrelevant because I encode), but because of the quality.
blksize=16 on 720p content is a great setting for most content IMO, while blksize=16 on 1080p content is worse, as is blksize=32 on 1080p content.
It didn't matter much to me before because I mostly watched 720p content, but now I am mostly watching 1080p content so I would like the same interpolation benefits I had with 720p content but with the resolution increase.