I have had some issues with 5.5. I was going to go back out this weekend to try it again but I got a dang crick in my neck and don't want the pain that will come along with driving the boat.
I don't have any lagging on SI; but I have severe issues with interference that I never had before.
I did have some lagging on 5.0 though.
I may end up going back a few updates if I still have problems, nothing on these new updates benefits me.