I have sailed both.
The W54 is very sweet with 6.2/7.0. Whereas the W49 6.2/55. Both can take one size bigger sail, but not ideal.
Guess it comes down to what sails you use more often.
The 49 would be the way to go as a one speed board solution.
Isonic 97 2013
JP Speed 50 2014
Severne Reflex 4 7.0,6.2,5.6