Running on IIS means you are never going to really see the proper speed of PHP as that just isn't a native platform it.
[clenches teeth] Have you checked out ASP and .NET as possibilities? [/clenches]
! that was horrible - advising use of asp
PHP would handle that easily - a distro framework with CMS and you're pretty much done - try googling 'ezPublish' or 'PHP CMS' and see what is available. I'd strongly reccommend seating that on an Apache server base, just so you don't get dissillusioned at PHPs speed when the IIS server is to blame.