Ok, well ill give it a try, if it doesn't work ill give the RAM to my brother's. Thanks for the reply!
If it doesn't work at 1866MT/s, you can try again at 1600 or 1333.
Large memory configurations (more DIMMs per channel) put extra load on the CPU's RAM control lines and that makes high RAM clock speeds more difficult if not impossible to achieve. If you look at motherboards' QVLs, you can see that the proportion of modules certified for dual DIMMs per channel goes down as frequency goes up.
The real-world performance difference between 1600 and 1066 is already not much with dual-channel memory so going from 1866 to 1333 on quad should hurt even less.