Fund costs vs. performance

[LRAO]

Hello once again.

When looking at funds to add to my portfolio, here's a question for you all:

How much more important are costs (loads/expense ratio) vs. performance?

I mean, if Vanguard has a fund that is NL with an ER of 0.20, but has returned 5% (annualized) over 10-years and Company X has a fund that is NL with an ER of 1.50, and has returned 11.5% over that same 10-year period, wouldn't it be THAT MUCH BETTER to bite the cost bullet with a proven winner?