It will fit but I'd worry that the motherboard won't like the 136W TDP or the 1600 MHz fSB (Non-extreme quads are 95W and 1333 Mhz) - the manual for the X3810 doesn't list any extreme parts in the appendices (http://www.manualslib.com/manual/1367/Acer-Aspire-X3810.html?page=104#manual)