We're building a social web 2.0 site and want to know if any of you would agree that the following CPC rates vs. impressions sounds reasonable:

1 million impressions/month = $0.20 CPC {20% of ad bid; Bid: $1.00}

5 million impressions/month = $0.50 CPC {25% of ad bid; Bid: $2.00}

18 million impressions/month = $1.50 CPC {30% of ad bid; Bid: $5}

45 million impressions/month = $4.50 CPC {45% of ad bid; Bid: $10}

70 million impressions/month = $7.50 CPC 50% of ad bid; Bid: $15}

Is this too conservative? liberal?

Any help would be greatly appreciated!
Thanks