Some mega-cap stocks and related exchange traded funds have been beacons of stability this year and that much is confirmed by the Guggenheim Russell Top 50 Mega Cap ETF (NYSEArca: XLG), which is up 2.8% year-to-date.

Some mega-cap ETFs may not provide too much diversification from some benchmarks. For instance, the Russell Top 50 Mega Cap Index, the underlying index for XLG, is almost perfectly correlated with the S&P 500 over the past 14 years.

Over the past 14 years, the Russell Top 50 Mega Cap has fallen behind the Russell 2000 index of small-cap stocks by an average 3.3 percentage points per year, The index, though, may offer cheaper valuations as it is now trading with a price-to-earnings ratio of 18 times, compared to 21 for the Russell 2000. Looking ahead, analysts expect a 9% earnings growth for the Russell Top 50 Mega Cap Index, compared to the 12 growth for Russell 2000 stocks.

While mega-caps may show slower growth, the asset category also come with lower volatility. Specifically, the Russell 50 Top Mega Cap Index has a standard deviation of 13.8% over the past 10 years, compared to a 19.5% deviation in small-cap stocks. In January, XLG will drop its current index in favor of an S&P index. XLG currently singles out the biggest U.S. company stocks taken from the the Russell 1000 large-cap index.