Google Adwords CPM campaigns

I’m experimenting with a CPM site-targetted campaign on Google Adwords and so far the results are promising. I have two campaigns advertising the same site one with a max CPC of 20¢ and the other with a max CPM of $2.00 targetted to a single site. So far the CPC campaign is producing more traffic, but it’s costing me on average 18¢ per click whereas the CPM campaign is only costing me 4¢ per click. I think because of my very selective targetting I’ve managed to find a site that has visitors looking for what I’m advertising, but not offering competition (hence a higher CTR and lower effective CPC). Google, Adwords