@wizofoz: technically speaking, you should have the tool to calculate takeoff-data for each CG position within the envelope. However, you legally might not be allowed to. On some Boeing aircraft (appendix to the AFM) you must decide on one (or two) distinct Alt FWD CG position(s). Your Boeing database will allow to calculate every position, but alas, legally you have to stick to the selected one(s).
@mj23:
Aft CG positions will lower fuel flow to a considerable amount.
Imagine the airplane to be a balance, hang up at the center of pressure (CoP). The center of gravity (CoG) for a typical airplane design is fwd of the CoP and thus, the weight induces a pitch down momentum. To out-balance this, your stabilizer has to create a downforce (pitch-up momentum). The farther your CoG goes aft (closer to CoP), the smaller is the pitch-down momentum induced by the weight. The smaller the pitch-down momentum is, the smaller the pitch-up momentum, induced by the stabilizer, has to be to keep the airplane balanced. Smaller pitch-up momentum means less downforce on the stabilizer.
The total lift, the wing has to produce, is the sum of the weight plus the downforce. Now, the lower the downforce is, the lower the total lift has to be for the same weight. Lower lift also means lower drag, which in turn means less fuel consumption.
I hope I could help a bit.