I'd say a X38, im pretty sure anything with a PCI-E 2.0 slot supports either crossfire or SLi, but nothing wrong with a extra PCI-e slot. PCI-E 2.0 is pretty useless right now either ways.
4 slots? as in 4 pcie slots for 4 vid cards? no such thing for intel.Only boards i know that have that are the 790fx or higher boards for Amd but then your bottlenecking the hell outta them with a phenom.