The motherboard is important in terms of the features you get (ports and expansion slots), as well as overclocking and similar performance tweaking.
It isn't really a brute performance thing, per se. Two chipsets running the same CPU at the same speed with the same RAM etc would give you the same performance, or perhaps a negligable, imperceptable difference. It's all about features, stability, support and customer service.
I've only used ASUS boards for the past decade, because they are very good at providing those four things.