There are a couple of different sweet spots. Not only is there a Max Feed Rate, there is a Max Acceleration and Jerk. You want the printer to move quickly but you also care about what the print looks like. If you only print round vases and flower holders and candlestick holders, you might be able to really crank up your feed rate because the acceleration is smooth the whole time. But if you print things with lots of sharp edges, it is possible you have to slow things down to make the print look good even if the machine doesn't lose position.

I would bump up (and down) the X & Y together. The Z doesn't really matter other than if you are printing on an unlevel bed with Auto Bed Leveling that can end up limiting the speed you go at if it isn't high enough. (The planner won't exceed the speed needed to do a move on any of the affected axis. If the Z can't move fast enough for what is being asked for in the X & Y, it can limit the speed. But the Z usually can tolerate speeds much higher than default.)