I always look at the reloading manual velocity as 'guideline'... Not what I am going to get over the chrono. Same with what you find in magazine articles. I shoot mostly revolvers and cylinder gap, bullet, primer, barrel length, temperature, etc. all play into what your velocity is really going to be. And in actuality, 'accuracy' in 'your' gun is more important than a few fps.... If going 3000fps puts them on a 12" circle at 200yards and 2900fps puts them all on a 4" circle and 2800fps on a 2" circle ... what would you use?
. That is what is called working up a load.... Not to see how fast you can go... but to see how accurate a load can be (within the min and max load data of course)!
[added] Note this only hypothetical, the groups could be decreasing as you go up in velocity or act like a bellows opening and closing...... Having fun yet?