well ok 21 mph seems a good speed for that set up and with 6 cells yes 25mph isnt out of the question
ok well just get some lithuim grease from a marina (just ask if they sell lithium grease) and that will be god for the lube . i also see you have a plastic prop , GET rid of that if you get a good brass one or carbon one you will get better preformance and speed

also if you dont have one already buy some 3300mah batteries for it you will get a lot longer runtime
have fun with the boat it will prefom welll for you, but if it doent go to a smaller prop
your run time will vary with a 3300mah pack you should get about 15 mins out of it , and rember it is all in how you drive it

oh and by the way fix the water cooling get a better water pick up from under the hull, and put more tubing around the motor to keep it cool, rember the cooler it is the longer it will last