They are about the same (3 x PBP, 1 x LEL). LEL is further and has some harsher terrain in the northern half, but has a more relaxed time limit so you have less night riding (especially not having to ride through the first night).
The variables (weather, personal condition, company, and general mental state) are much bigger.
PBP 2007 - atrocious weather, great mental state - easier than PBP2011 - good conditions poor mental state excacerbated by ambitious target
PBP 2015 great weather, great mental state - easier than LEL2009 - atrocious weather, moderate mental state, great company
PBP2007 + LEL2009 - recall for Noah - equal difficulty.