How hot can you go?

I have used all types of PMC. However, I was not careful about keeping track of the clay type, i.e. PMC, PMC+, etc. So, I no longer know which lump is of what type.

I am thinking the amount of shrinkage and firing time is determined by the "binder" and that the metal itself should be able to take the highest firing regardless of the binder. Are my thoughts correct? If yes, when using Art Clay, that might also get mixed with my other "lumps of PMC" the firing temp. should be all right at the highest and longest firing time. Yes? :0)

[Metalman]

I think your thinking is correct here but then that leaves you firing everything for 2 hrs at what, about 1650°F?  Torch firing might be an alternative but I am unsure if torch firing works with original PMC.
Just a further note - I think that the shrinkage and firing time is related to the particle size. It was my understanding that original PMC was graded at 20 microns and it was the spaces between particles that caused the shrinkage. When the material has a broader mix of particle sizes, the spaces are filled to a higher degree and - hence less shrinkage.

Regarding containers of clay, etc.  I use plastic cosmetic containers with internal sponges [R&T# 69-132] for moisture maintenance.  Permanent markers and white-out pens work for marking the container.  Both of these materials clean off with alcohol when I need to change the labeling.  This way I can keep track of the multitude of mixes and materials on my bench.