I added a second graphics card to my garage PC yesterday, it still has the old Quadro 2000 for CAD use but has a GeForce GTX 750 Ti gaming card now as well. I picked it up second hand, I know they're not particularly new or powerful by todays standards but it runs Zwift in 1080p very smoothly. Not sure what the frame rate is but it seems good. It runs it in Ultra mode fairly well, but since the beamer is only 800x600 it seems a bit pointless rendering it in UHD so I've scaled it back 
The PC itself is pretty powerful, its a quad core Xeon 3.2GHz, 8GB RAM. It loads Zwift pretty quickly, about 15 seconds I would guess. Solid state hard drive too which I'm sure helps. Being a CAD user at work certainly has benefits, it was my work machine and I picked it up free when it had come to the end of its useful life about 4 years ago. The PC now in my study was it's replacement and I took it home last year for the same reason, it's a quad core Xeon 3.6GHz, 32GB RAM and a Quadro 4000 graphics card
It'll likely be the last freebie I get as they've moved to leasing their hardware so it will probably not end up in the garage on Zwift duties any time soon 

The PC itself is pretty powerful, its a quad core Xeon 3.2GHz, 8GB RAM. It loads Zwift pretty quickly, about 15 seconds I would guess. Solid state hard drive too which I'm sure helps. Being a CAD user at work certainly has benefits, it was my work machine and I picked it up free when it had come to the end of its useful life about 4 years ago. The PC now in my study was it's replacement and I took it home last year for the same reason, it's a quad core Xeon 3.6GHz, 32GB RAM and a Quadro 4000 graphics card

