At 5'8" you'd definitely be on one of the 26" LHT's which will work out great. 56 would be too big.
You're either a 52 or 54. See if you can find out what your standover clearance is. Get a book, and stand to a wall with your back against the wall, put the book between your legs and up against your pelvic bone. Mark that spot on the wall and measure it. Make sure to do it on a hard floor surface, not carpet.
I'm thinking you'll be a 52