Exceeding your mobo ram limit can go one of many ways.
1. It recognizes it and runs it like there is no limit. (If you're lucky.)
2. It recognizes it, underclocks it and utilizes all 8 gigs. (Less likely but could happen.)
3. It recognizes only some of it (i.e. 4 instead of 8). (Likely.)
4. It won't boot at all. (Not a catstrophic, breaking kind of wont boot... it just wont post.) (Doubtful.)
My motherboard is rated at 4gb and I run 6gb. So it is possible. But my mobo is a pos and underclocks all ram.