Most often think that higher veloity means extra range/effective distance, when it really doesn't at all. A lot of newer players shoot for 400fps as a arget, not taking into account that velocities can vary from day to day and air/temp conditions, so they are risking not being allowed to play in order to feel good about being able to match better players simply because they think all the great players run 400fps guns and that is why the great players are great.
I'll say this, I'm a level 3 certified sniper in Canada, instructor status as well, and am rated safe up to 600fps in some game places, and have tried out all kinds of velocities with heavy BBs. Why have I been using my M24 rifle all year set at 397fps with 0.20g? Because it's the best I've ever had that rifle shoot. And at that velocity with 0.20g, I use 0.36g BBs all the time in my rifle, even knowing they are flying out the muzzle at ~300fps. My field MP5SD is set up at 370fps and works great, much better than it did close to 400fps last year. Nutshell, brains will always outdo upgrades.