We have 265 hours of surfing in on our 2012 X-25. We experimented this year with filling the KGB tank to 50% (as opposed to 100%) for riding either side. Didn't make a difference - so we now only fill the KGB to 50%, which makes that end of the day dump just a little quicker.
We also have the bow filler cushion and I keep a 260lb sac under it. It extends the wave nicely and isn't in the way at all. I like weighting the bow. 540lbs is plenty of weight up there.
For our rear ballast, we have 750lb sacs in each locker. You might want to replace your 450's with 750's. Big difference there (I have tried 400 in the lockers and felt it wasn't enough).
Bottom line is that the X-25 is an excellent surfing boat with a ton of options for creating different wave sizes and shapes.