I agree withe the sage advice from Bill, Trix and Gene. My personal take is to do exactly what Bill listed, but buy and I7 if you can afford it to future-proof your machine. I was using an I5 (iMac) but now use a Xenon iMac Pro, both with 32GB of memory. The new machine is faster, but may not be needed by you and it wasn't cheap either(5k). I am a pro and process almost every day. This machine saves me some time, so it is very important to me. Best of luck.
The iMac Pro is a fine, fast machine, especially the way you loaded it. And YES, you can justify the extra cost when you can move images out the door or onto the Web more quickly.
18 years ago, I worked in a photo lab where we were just transitioning everything to digital imaging processes. We were using dual processor (not dual core) Dell Zeons that cost a small fortune. We had four of them that rendered images 24/7, with no breaks! Today, one good iMac or PC could probably beat those four Dells in 8 hours. We have come a LONG way. And still, the speed race continues.