You can set pitches to go up to 127 mph, although they actually top out a bit below that. The funny thing is that when you set things up that way, it doesn't seem to have a ton of impact that's so different from the regular speeds. Batters -- even bad ones -- can smack your 114 mph heater right over the wall, so there must be some element where the program compensates for the difference. One good reason to throw pitches in the 110+ mph range is simply to hear that cool sound of the loud pop when the catcher receives the pitch in his mitt.
You can set pitches to go slower also, but not to the same extreme. If you set your changeup to be 50 mph, 30mph or even just 1 mph, you still won't get any pitches to go much slower than about 57 or 58 mph.
You can change the break and angle of pitches very drastically. You can make it so that you need to move the left stick as far to the upper right or left corner as it will go while aiming in order to get a pitch any where near the strike zone. You need to do some significant tinkering with those settings to figure out what you're looking for. The one thing about messing with the pitches in this way is that it doesn't just apply to you, but to the CPU pitchers as well. If you make it so that a certain pitch flies in a wild fashion towards the plate with tons of movement changing direction more than once during its flight, you may be able to learn how to use the pitch effectively in time, but as soon as you change those settings, any pitcher you oppose will have the same action when he throws that pitch, and it seems that the CPU knows how to make those kinds of pitches work properly right away... you can see some funky movement on pitches being delivered to you while hitting.