Top flight ATI cards? the only ATI cards that can compete with the above card i posted would be the new r600, that will be faster but it will also cost alot more no dout.
Trust me you will be blown away with any 8800 series card, and it WILL run anything out today at max settings(providing you dont have a 30" screen or something ridiculous)

By the way you definatly wont get the best from the card until you upgrade but it will still kick some ass