Can I get 4GB Memory with DK790GX PlatinumI?

I am running OCZ Reapers 2 x 2GB (OCZ2RPR10664GK) on 1.8 V rated modules on the motherboard. The specs call for 2.1 - 2.2 V to power them. In the BIOS I changed the voltage to match those settings. My maximum bandwidth is stated at PC-6400 (400 Mhz) from CPU-Z whether or not I have the voltage set at 2.1 - 2.2 v or 1.8 V. Under the BIOS I changed the EPP setting from disabled to enabled and it changed from 800 Mhz to 1066 Mhz. Also when I run System Performance Report through Vista Ultimate x64 it says at most I get is 2935 MB available for memory at 2.2 V EPP enabled. With it set at 1.8 V EPP enabled I get 2574 MB available memory. Is there any way I can get the full 4 GB or get it closer from the 2.9 GB I get now. Also I was curious to how the increased voltage can damage the motherboard, in the bios it says the max rating is 2.5 V and at 2.2 V the system may run unsteady.