I have been managing PC builds for our office for several years. We have a dozen seats of Solidworks with some simulation softwares. For productivity, we ditched the ECC requirement for faster compute... We ended up with overclocked mainstream cpu 2700K, 3770K and I'll continue with 6700K. The $$ saved from not going ECC goes into SSD and other productivity "enhancer". Staff wait less, they are happier, complain less about PC freezing over and over. Then, do we have memory issues, surely, I mean, I don't have ways to measure it, but if somebody raised a hand and say that he takes the same file twice from the server and once it works, once it crash, we know there is an issue somewhere. But it never seems to happen consistently enough that it hinders productivity. Plus... I am not building rockets...
If you browse through solidworks own forum (not sure it's open to public) you will see a lot of report of people moving to mainstream overclocked cpu + professional card.
For the server side... YES, ECC everywhere, Xeon (or the equivalent AMD) everywhere, redundancy like our life depends on it... that, we can't screw up.