This question is asked heaps in various ways. I have experimented with both forms of advertising on my sites over the years and in the end PPC seemed to out perform CPM adverts every time without question. Early in my site developing days I saw CPM as the best answer to my horrific PPC CTR but as my ad placement, implementation and ad management strategies matured I saw that PPC advertising was really the hero with a much better return than CPM could every bring. I knocked up an article today about choosing PPC or CPM, but would be very interested to hear what others have to say about this subject. I use both PPC & CPM these days but the CPM ads are used very sparingly on my sites these days.
I think it depends on the sites topic, how well your optimize the ads into your web pages and your type of traffic.
Although I have never tried this myself I think you may be right there but I only ever compared one cpm banner to one ppc banner. The problem with your suggestion is that it would be pimping out your site out and making it look spammy with heaps of cpm banners, which I think is not worth it unless you have a site that just gives away free downloads or something that does not require repeat visits etc. "just my thoughts"
i agree with john... it really depend on the site, traffic and the ad network.... so why dont you post the details...