Hi,
We don't use CMIS, so cannot help there. Would guess that it's as easy to integrate CMIS as SIMS was ))))
We are using Class and Portal. All of our staff use it; forced to by GPO, and again all of our students use it. Some staff (10) use class server to post assignments and homework exercises; all staff and students are moving to our internally hosted exchange email in September. Its been launched for about a year now and so far (barring) a few teething stresses, no real issues.
We trialled SWGFL portal; not for us, we trialled Moodle; not quite flexible enough for us; and we looked at sims gateway; but not ready in time.
Sharepoint is expensive and complex; but if you do the homework and read; its easy enough.