I got rid of my PRO-1 and bought the PRO-1000 because I felt I was wasting so much ink every time I went to print. (Though I tried to be diligent and print something every few days, the reality was, it didn't happen. So the PRO-1 would purge and purge and purge and clean.
I have an iPF8400 as well. I feel it too is better about inks, even when I haven't printed in a while. I bought the PRO-1000 in November and bought extra ink carts. Though I haven't printed a ton, I'm still using the original carts!