I thought the chance was about the same though. That even though its a higher percent chance to proc with a slower weapon, you end up with less hits for it to proc off of. In the end it evens itself out because [less hits * better proc chance] = [more hits * worse proc chance].
Though someone should really check the math and find out.....
At least this is the way it is with Crusader, and I believe Landslide procs the same way. Elemental force is dependent on the time in between attacks and haste. So if you want to find the ample weapon speed between MH, OH, & special attacks (...lol...) knock yourself out.