Maybe not the answer you want, since it is a question.
Are they looking for lots of manual interaction or mainly straight-through-processing? A major difference, since in the latter, the ui delay can be a major contributor in the overall performance. Besides that, the complexity of the actions carried out with each step can influence the overall performance as well. These issues should be answered by the companies giving answers to your questions.
Yes, good questions. Only wish I had all the answers ;-) I don't yet know the specifics about their intended processes only that they are looking to obtain performance data from existing users so that they can avoid going through a lengthy internal performance testing project. I would assume that any internal testing will be primarily straight-thru processing and generally carrying out simple actions.
I will check with the sales rep to see if he knows of any specific requirements.
While we're on the subject, does anyone know of any public BPM performance benchmarks or is it only ever done on a company-by-company basis?