the problem with the 04 kxfs and rmzs is that the oil filter and water pump share the same cover and because of this, they overheat because the impeller on the waterpump is too small. plus everytime you have to change your oil filter you have to flush your radiator. but this can be fixed by buying a boyesen cover that is 2 peices and it has a bigger impeller on the water pump. its about $180 or so
another way to get more low end power for less money is gearing your bike down. go up 2 teeth on the rear sprocket or drop one tooth in the front. That will put more of the powerband's power in the bottom end.