I would personally just let him purchase the card he wants, which is the GFFX. If you talk him out of it, he will blame you for each and every thing he finds wrong with the ATI board. No matter what it is he will say stuff like "I wouldn't be having this problem if I had purchased the GFFX like I wanted to in the first place". The first EA game he plays, he will blame you for having to wait for the game patch before the game is playable.
AIW 9700 Pro | 1.3GHz CeleronT | 512MB PC133 SDRAM | ECS PCIPAT Mobo (Intel 815EP)