Different between medium curing bitumen MC-30 and MC-70

[defg]

I have come across some various road projects,where the medium curing grade is applied with respect to weather condtion(climatical condition).This MC-30 is normaly applied in moderate cold regions because of its viscous properties while MC-70 is normaly preferred in hot and dry regions.In our specification require the Contractor to use MC-70 for primming works as the project road is found in dry and hot climatic condition.The Contractor is asking for a permission to use MC-30 instead of MC-70.Iwent through the testing manual (AASHTO M82-75(1993)and found that most of the properties requrement,min.and max. are same except the following tests:
Kinematic viscosity at 60Centigrade(MC-30, 30min and 60max.MC-70,70min and 140max
Distilate,percentage by volume of total distilate to 360Centigrade
Residue from distillation to 360Centigrade.
Is it possible to allow the Contractor to use MC-30 instead of MC-70 as specified?OR there will be detrimental deffect!Please assist