The 904 kit will transform the bike into a completely different machine. There is a huge and very noticable increase in the performance. The HP and torque both go up substantially. it is well worth the money to do to a 790 motor, not so much with the 865 though. Another thing to be sure to do is to have the intake and exhaust cleaned up while it is apart. getting the rough spots ground away helps the fuel flow much better giving a smoother response. This is just a bit more $$ but in my opinion it is s must do if you're already into the motor. Just don't make it too smooth, it needs some turbulence to get the air and fuel mixed properly. Any decent engine shop can do this for you.
