Where exactly did you read that a cheap motherboard will slow down your computer?
A motherboard is a pretty stupid thing, it just takes data from thing A and moves it to thing B. That is about it if you really boil it down.
For the most part, one board is as good as another at doing that basic task.
The best reason to spend a lot on a motherboard is if you know you need whatever it has that a cheaper one doesn't have.
A cheaper board may limit how much you can OC your computer, is that something you intend to get heavily into?