Agreed. It's all about adaptation to the frequency.
It's the same principle why newbs do 1 bodypart a week, get sore as hell, and think they blasted the sh*t outta their muscles, and wait another week to do 'em again.
If I were you, I would work my way up to 3x a week before starting the 5x5, albeit with lighter weights. Get your body used to the frequency first.
If you do this for two or three weeks prior, you will not be as sore (if at all) come 5x5 time, even as you increase weights.