Yep, this beta is having issues with transparency
Tree with transparency issue in beta 4.5
Same tree in beta 2
Stock leafy bush in beta 4.5
Stock leafy bush in beta 2
It's as though there is some kind of layering of the alpha channel and diffuse with multiple render passes being offset. You can see this in the first tree screenshot at top right of image. It may doing this with all textures and only noticed with transparency, which might explain the fps drop for many with this beta
Player speed in test level is way fast.