The speed it shows in your bios is the true speed. The "DRAM Frequency" it shows in CPU-Z is half of the speed so you have to multiply that by 2 to get your actual speed.
Since your motherboard only supports dual channel 2 sticks will run in dual channel and the other 4GB will run in single channel. (if i'm wrong someone will correct me but i'm pretty sure that's how it works)
Also yes it is fine that your ram voltage is higher than your CPU voltage 1.5V is the proper voltage for that RAM.
Everything looks good!