So far I have never seen a laptop that has the 950m and uses DDR5 RAM. Since Acer tends to sell pretty inexpensive laptops I am positive they do are not using DDR5 RAM.
The desktop Radeon HD 6670 was released in 2011 which had DDR3 and DDR5 variants. Based on some benchmarks the DDR3 version was about 20% - 25% less powerful than the DDR5 version. Compared to current laptop GPUs I would say the Radoen HD 6670 DDR5 is definitely more powerful than the nVidia 940m.