Smooth filterable portfolio

Smooth filterable portfolio

I'm trying to work with this filterable portfolio, but for my needs the
transitions are not smooth enough.
JS
var Portfolio = {
sort: function(items) {
items.show();
$('#portfolio-content').find('div.portfolio-item').not(items).fadeOut(500);
},
showAll: function(items) {
items.fadeIn(500);
},
doSort: function() {
$('a', '#portfolio-sort').on('click', function() {
var $a = $(this);
if (!$a.is('#all')) {
var items = $('div[data-cat=' + $a.data('cat') + ']',
'#portfolio-content');
Portfolio.sort(items);
} else {
Portfolio.showAll($('div.portfolio-item', '#portfolio-content'));
}
});
}
};
Portfolio.doSort();
HTML
<div id="portfolio">
<div id="portfolio-sort">
<a href="#" id="all">ALL</a>
<a href="#" data-cat="a">A</a>
<a href="#" data-cat="b">B</a>
<a href="#" data-cat="c">C</a>
</div>
<div id="portfolio-content">
<div class="portfolio-item" data-cat="a">A</div>
<div class="portfolio-item" data-cat="b">B</div>
<div class="portfolio-item" data-cat="c">C</div>
<div class="portfolio-item" data-cat="c">C</div>
<div class="portfolio-item" data-cat="b">B</div>
<div class="portfolio-item" data-cat="a">A</div>
<div class="portfolio-item" data-cat="a">A</div>
<div class="portfolio-item" data-cat="c">C</div>
<div class="portfolio-item" data-cat="b">B</div>
</div>
CSS
#portfolio {
width: 100%;
max-width: 600px;
margin: 2em auto;
}
#portfolio-sort {
text-align: center;
padding-bottom: 3px;
border-bottom: 1px solid #999;
margin-bottom: 1em;
}
#portfolio-sort a {
color: #fff;
background: #a00;
display: inline-block;
padding: 3px 9px;
text-decoration: none;
margin-right: 1em;
}
#portfolio-content {
overflow: hidden;
}
div.portfolio-item {
float: left;
margin: 0 3% 1em 0;
width: 29%;
height: 10em;
line-height: 10;
text-align: center;
}
div[data-cat="a"] {
background: #ccc;
}
div[data-cat="b"] {
background: #666;
color: #fff;
}
div[data-cat="c"] {
background: #333;
color: #fff;
}
Is there a way to make the filtering smoother using CSS3 or jQuery?
Here is the complete code: http://jsfiddle.net/gabrieleromanato/KkxyS/