I just had a quick look at the LivePreview but couldn't get it working with a Contax.
The Contax must be set to "B" mode.
By accident I had one single preview that infact looked somehow like an "image"... but cut in the middle, like a sync error.
Maybe it was just me ... I am going to figure out how it works, if it works at all.
Anything else goes pretty well with V5 here. Tethered shooting as in V4, no problems. But I don't shoot high volumes with high frame rates.
Workflow wise it's an improved V3 now... pretty much.