E5-2670s <$90 was a huge discount - and I'm get 32~33K on GeekBench multi with two of em.
Asus ROG Zeneith and X399-E motherboards support ECC UnBuffered which is $97 ~ $115 / 16GB 2400 MHz at the moment.
Kingston Technology ValueRAM DDR4 ECC CL17 DIMM 1Rx8 Micron A Server Premier Memory (KVR24E17S8/8MA) at Amazon.com $97
Its not going to beat DDR3 prices, but personally I dont see the value in getting HW 3 generations old unless its at a significant discount and performance + power is not more than 30% difference. If you need more than 128 GB than that is a limiting factor, I'm running 256 GB right now and its great.
Do agree that better mobos will be coming out and making things much nicer. Past V2 E5's Xeon had no real competition so they are not very impressive products. Most companies I know held off on their upgrade cycle because V3 and V4 weren't significantly better for OpEx.