The voltage difference isn't a real problem,but adding ram can give problems. Only thing you really can do is try it out. See if it works. Can do a night of memtest to see if it is stable.
You can look in the bios if both sets run at same settings,check the voltage since one of the sets needs 1.35V where the other can work at 1.25V,make sure ram is working at 1.35V.
The voltage difference isn't a real problem,but adding ram can give problems. Only thing you really can do is try it out. See if it works. Can do a night of memtest to see if it is stable.
You can look in the bios if both sets run at same settings,check the voltage since one of the sets needs 1.35V where the other can work at 1.25V,make sure ram is working at 1.35V.