Cat 1 vs. Cat 1 modified vs. Cat 0

[bx24d]

I'm looking at upgrading my sears garden tractor to a four wheel drive garden tractor or sub compact. My new purchase will have four wheel drive, shaft drive to the wheels and mower deck and a diesel engine. I have a compact tractor but having a PTO on the new mower will give me more versatility. The options I'm looking at include category one and cat 1 modified. I think the cat 1 modified has cat 1 dimensions but a smaller PTO drive shaft.
Is this correct? What type of implements can be run off this smaller shaft?

Before I purchase anything other than a true cat 1, I want to know the capabilities and the ability I will have in using the three point equipment I own already

 

[crabjoe]

I think the difference between them are lifting height. A Modified Cat 1 can't lift to the same height as a true Cat 1.

 

[ChallengerMT265B]

I think Cat 1 with 1 3/8 540 pto will give the best resale. With more implements (new & used) to pick from.

 

[Soundguy]

Lift categories won't change pto stub size. It will effect lift arm spacing.

Soundguy