I bought the 27" 3.4GHZ 2GB VRAM with the 3 TB fusion drive....it replaced a 2011 maxed out model, and also benefits from 32GB of RAM. The extra power is what I've become used to, and the better, faster shortage option is a great help too.
I would have liked the large SSD, but decided that I really couldn't justify the extra expense. I have plenty of off Mac storage available, and I couldn't be happier with my new ( January) iMac.🙂