An 8% CTR seems very high to me, but I suppose it's possible that the ads are just that well targeted to your users. I typically get a CTR of about 0.5% for banners and 1.5% for interstitials, though it varies.
Is 500K/day the number of requests you are generating? This doesn't seem to mesh with the 250 impressions per week.
One of these numbers just doesn't belong here.
William