I'm currently running on a late 2015 iMac (27" 5K Retina, 3.2 GHz Intel Core i5) 32GB RAM and 1TB fusion drive. Runs super duper fast and smooth.
But... prior to this I was also running on a late 2009 iMac with 16GB RAM and a 512K Fusion Drive... still ran very well for me.
Go as high as you can with your budget... realize the return on investment, as sometimes that's hard to measure when looking for a machine to run software. Think of the time savings and frustration savings...