Have you considered a 2018 Mac Mini?
It should be more than adequate to drive your existing displays and it's a heck of a lot cheaper than your other options.
May not be great for games - all depends which games you want to play.
As far as the Mini is concerned- are there any rumours about a newer version on the horizon?
That may be another option if you don't need to get a new Mac right now.
I have looked at Mac Mini's and searched the net for any rumors about any new Macs coming out soon. No solid info. A Mac Mini i5 with 512GB SSD and 8GB RAM is $1099 but is out of stock at BestBuy but available in 2 days from Apple. I prefer to get my Mac from BestBuy since they're just around the corner and I can get 1yr same as cash but it's not a big deal.
And unlike my late 2012 Mini the RAM is a major PITA to upgrade, you have to pull the logic board out. The 2012 took me all of 5 minutes to upgrade RAM. I've have to take the 2018 to Experimax and let the pro do it. And probably void my warranty. Now the UHD 630 will support up to 3 monitors. Running 2 I could do:
5120x2880 at 60 Hz via Thunderbolt 3 and one display up to 4096x2160 at 60 Hz via HDMI 2.0. (Thanks to EveryMac.com for that info)
For about the same price as the basic 27" iMac I could get an i7 Mini with 16GB RAM and a 1TB SSD from Apple ($1699) with about 10 days for delivery.
I need to decide if I'll ever want to use the new Mac for any gaming other than simple card games, pinball, etc which I'm playing now on the 2012 Mini. If I don't then the Mini would work and the i7 version has nicer specs than the iMac. 16GB of RAM should be enough.
So the Mini would be $100 cheaper than the basic iMac, give me a 1TB SSD vs. 1TB Fusion and 8GB more RAM (worth ~$40) and an i7 vs. i5 CPU.
Again using Geekbench numbers off of everymac's comparison page the i7 Mini has a significant advantage over the base 27" iMac. It's definitely something to think about and would be easy to switch out.
You guys think this is bad you should see me when I car shop..........