In my free time, I've been building a quick test project to benchmark different ways of handling transform data in Vulkan.

I've posted a write up of the results of that benchmark on my blog:

http://kylehalladay.com/blog/tutorial/vulkan/2018/03/27/SSBO-VS-Uniform-Buffer.html

Key takeaway - push constants don't scale as well as UBOs or SSBOs when you're talking about tens of thousands of meshes.