To the OP: You really need to speak with Tony about this. You are getting a big range of opinions, (and some bad information). Short of that find a shop that stocks IROs and test ride one if you can.

My money is still on the 59cm but the 56cm could work also. The 53cm is out of the question too small. Period. Basically, subtract 3cm from the stated IRO fit to normalize it to other bikes. So the 59 is essentially a 56, the 56 is a 53, and the 53 is a 50!!. You are absolutely too large for a 50cm frame.