I was fit today for a new Titleist U510 - 4 90gram x smoke.
During the fitting (on a trackman) I hit my Mizuno mp15 5, 4 and 3 iron to identify gaps. I came in because I FELT like I hit my 4 and 3 iron the same distance.
As it turned out, my 4 iron averaged 197y carry with a 1.44 smash factor and a landing angle of 42 degrees. My 3 iron was longer, but averaged about 204y carry, but on a 1.37 smash factor and most importantly a 38.5 degree landing angle. If we took out the poorly struck shots and only included 1.4+ smash factor, my three iron WAS longer with a 209y average carry and landing angle of 40.5.
However, when I hit the 510u 4 iron my average distance was 216 with a landing angle of 44 degrees. My dispersion was tighter, the ball flew higher and my distance was much more consistent.
I very much preferred the look and feel of the 500u (smaller profile), but look and feel don't win golf tournaments, results do and the 510 had better results, bottom line.
When it gets in I'll post pictures, but thought the process was post worthy. If you are looking for a long iron replacement, I would definitely give these a look.