you have to remember that you can walk up to anyone on the street and say "do you who RTE is" probably a 100% yes rate

You cant compare rates for a national brand compared to a new venture.

So yes those rates are realistic for major companies/brands but not for start ups. And conversions tend to be in my experience far better from sites which have a trusted/loyal userbase even though the CPMs can be silly

For a new project like you are talking about, if focussing on advertisers for teh site I would give the emails as a "bonus" add on or sell them on a fixed sponsorship basis while you build trust with the advertiser and build up your user profile

If you are working on a niche and can build on that niche in terms of userbase, you will be able to get good rates (in time) but probably not as high the likes of RTE

My 2 cents