I've been using full beds of Evo-Hex. When I ordered my reel of Evo-Hex from GGT I asked about the differences between the various MSV strings. I was told that anything w/ "Evo" in the name has a softer outer coating which makes it not only softer but it will also remains elastic (I have one set installed w/ about 40 hours on it and it's still elastic but control is long gone) and does not stiffen like most other poly. However, the softer coating is not as slippery so it does not snap back as well thus possibly reducing spin.
There's no Evo Soft, just Focus Hex Soft, which I'm told is between Focus and Evo in softness and does not have the softer outer coating like the Evo.