Quick notes : you need to use the ACE for loading whatever payload you want (you can also edit in FSX but I find it less easy/practical) and then use FSX for adjusting the fuel load. So for each of the 757 variants above you will find the last three lines of each block :
a)Full fuel and max payload
b)Full payload
c)Max fuel at full payload

right from these lines you will find what are the figures to use in ACE to come directly to these figures, and also how to fill the tanks in FSX to come directly to the MTOW without too much tweaking... 

I hope you find it usefull. Notice the differences between the 3 models, in particular empty weights and corresponding MZFW...

PS : I will post the same info for the 767 in the 767 thread.