Questionnaire for determining usability of a system

As part of a pitch, business are determining the usability of two software products and have come up with a questionnaire to ask a set of end users.

They have asked me to feedback on the questionnaire and I said I will come up with 5-10 questions that variously test the usability of the two software systems.

The software systems are document search and markup applications.

My question is: what are the best questions to ask?

At the minute I'm seeking answers to how learnable the software is, how easy it is to perform common actions, how fast users can perform common actions etc

EDIT

As I think of it, the questionnaire should be voiced "comparing the two systems, which one did you find the easiest to learn? Why?"