Volatility in Limit Hold'em

I have heard it said that volatility is higher in LHE than in NLHE, given the tendency for more players to see showdown. Therefore, you will tend to win fewer pots but the pots will be larger. Does anyone have any data/research to back this up - which is more volatile, LHE or NLHE?

Further, in LHE, statistically how long can someone run cold? I.e., how long can a good poker player lose money due to bad luck (poor cards), before statistically his luck should turn. Any statistics/research that would suggest how long you can run cold?