I've just this minute got off the phone with the guy who sold me his Husaberg 550.
He bought his 570 on a whim and actually tried to sell me his 570 to keep the 550.
He said he went out for a ride last weekend, trying each of the 'modes', got back to his car and laughed to himself, wondering why the feck he sold the 550 which he said had much better power delivery.

The old ones also much cheaper, parts easier to get, easier to work on etc etc.
I was out last week on my 550 with a mate on his 570, we didn't swop bikes so couldn't give you my thoughts....which would be bias towards the 550 anyway