Can I Mix 1.65v Ram with 1.8v Ram in SB?

Hello community,

My current rig is:
2500K @ 4.5ghz
Asus P8Z68-v Pro
2x2Gb DDR3 1600Mhz CL7 (7x7x7x24) 1.65v (from my previous i5 750 Rig, ence the 1.65 voltage, but I´ve been running it at 1.6v with advertised 7x7x7x24 latency and it just works!)
2 x gtx570 in Sli
Vertex 3 120Gb
Corsair 750w, etc.

I use it manly for heavy gaming (Batman, BF3, etc). I ´ve been thinking about adding more ram and found this used kit for 15€:

2GB (2x1024MB) D/C Kit PN - OCZ3P16002GK
1600MHz DDR3* CL 7-7-7-24(CAS-TRCD-TRP-TRAS)
Lifetime Warranty 1.7 Volts 240Pin DIMM
Special Features 1.8 Volts EVP***

It is my understanding that this Ram is from the Core2 duo generation, and that the 7x7x7x24 latency is acomplished at 1.8v, but correct me if I´m wrong. I´ve been searching for a cheap way to add more ram and for a ram with similar speed and latency to my current one.
So my questions are:

- Do you believe I can I mix this 2 kits? Will the 1.8v ram run at 1.65v with the advirtised speed and latency or should I just buy a 2x4Gb 1.5v 1600Mhz CL9 new kit for 50€?
- Is it worth it and will i see real performance gains upgrading from 4Gb to 6Gb or even 8Gb, in windows and in games? What´s your personal experience?

Thanks in advance, guys!
Cheers,
André

I wouldn't. Because you are using a SB CPU, you need low voltage memory. If you don't, you will literally burn out the pins on your CPU. 1.65v was max for the old/original core series, the new SB based chips need 1.5v max. Because of this I'm not sure I'd even be running the ones you are, and certainly wouldn't run a 1.7 or 1.8v kit.