I have been running in Mizuno Wave Catalyst for years, and this is my 3rd pair.  I am the 'perfect' size 10, but the Wave Catalyst 2 in 10 was huge!  It was a full 1" longer than my other shoes.  I don't know what happened, but the sizing between this model and the last edition has changed dramatically.  I returned the size 10 and ordered a 9.5.  These fit, but they still feel a little awkward.
The good news is that these are still phenomenal running shoes.  They are very, very hard to wear out (tread, upper, or cushioning).  My first run was 11miles, and I never thought about my feet or shoes.  I love Mizunos.  Not sure what's going on with their sizing, but if you find a pair that fit, your feet will be very happy!