That longer tube does wonders for that Lil' Gun load, doesn't it! Take it on up to maximum published data if you don't see any signs of pressure along the way. (Which I doubt you will!)
You will be surprised at how well that little bugger performs!

Here is that video of me shooting a hedge apple with my wife's Marlin. The load is the one that Brian Pearce published in a Rifle Magazine article on the 357Mag Marlins.

Gotta click on it to watch it: (50 yards)