You have to look at both the DRAM/DIMM V and the QPI/Vtt V. You are correct that the DRAM V max is 1.65V. There's plenty of good RAM out there that can run at 1.5V, some so-called "performance" RAM may be spec'ed at 1.65V. Your QPI/Vtt will probably be defaulting to 1.1V. You may need to bump that up to get 8 GBs stable. 1.15V is a good, first setting to try.