They both have multiple PCIe x16 ports and can do CF/SLI with the provision that second and additional GPU uses lower speeds. That makes for some although little graphic performance drop. That may depend on processor too but I don't think it would be noticeable.
I would give Gigabyte one a slight preference on account of durability and partly looks. Don't have hands on with either but by experience and comments on internet Asus usually have better BIOS while Gigabyte MBs are usually more robust.
Both have good VRMs and cooling so are nicely overclockable providing CPU is too. Gigabyte one has newer CODEC sound chip but potentially troublesome "Killer" Lan.
Might be best to look up some recensions and benchmarks for either one but not from sites that sell them, they tend either to favor some or plainly don't know what they are talking about.