I should follow that up to say the only evidence I have for my "9 times out of 10" figure is my own anecdotal experience... which is just that. So take that for what it's worth.
All I can say is that I've had really good success getting dual channel running on mix and match DDR3 sets... but success has always come with bog-standard RAM (used to be 1333mhz, more recently 1600mhz for DDR3), with thoroughly normal voltages and subtimings - which I've always matched carefully when buying new sets. Maybe I've just been really lucky, I don't know. But I tend to think it's worth a shot in your situation, given you seem to have a pretty standard 8GB 1.5V 1600mhz CAS11 DIMM.
But of course... get another Crucial DIMM and match those specs...