800X will give you near maximum velocities but it is a royal pain to work with.  It doesn't meter in most powder measures so you have to hand weigh each charge.  It also seems to get a little flaky when you get close to maximum.  Longshot is real easy to meter and should get you to your target velocity without going over "book" loads.  Start with about 8.5 grains of Longshot and work towards 9.5.  You should get to 1,300 fps somewhere in between.