Yeah the 5.5L is a toned down 5.5R. Less wheel spin the better.
Not only that but it's a couple of grams lighter as well.
There's a few that run the 5.5R at my track, but I've just stuck with a 6.5L.
I'm sure if I went to a 5.5 they would just run a 4.5, to have an edge on me.