I would bet the 23 is right... The 25 may be too aggressive of a pitch. I have a 500HP running a 24 (4 blade) I can't imagine you needing more then a 23.
Please let us know what you end up with.
Check out
http://www.offshoreonly.com/forums/prop-talk-165/
If you start a thread there I am sure you will get a lot of good advice on props and tests.
Good luck