Thanks for help. I know the PMDG model for the 400D has a much lower MTOW and I think a lower MZFW but not sure when it comes to fuel burn what the difference is or how well it's modeled in PMDG. In the FMC for the 400D it will let you load up to around 400,000LBS of fuel however you can really only load around 200,000LBS max without going over the MTOW if your also flying with a low ZFW and even less with more weight. I don't mind using the data for the 400 and just editing the weights as long as it will be accurate enough but not sure how well it will work since I plan to do flights at much lower weights and on longer routes that what it was meant for.