Add a Roamio or a Mini?

I'm having my basement finished and I currently have a TiVoHD upstairs, plus a series 2 TiVo. The basement will need another TiVo. I'm trying to decide between replacing the TiVoHD with a Roamio and buying a Mini for the basement or simply adding a Roamio in the basement. What is the video quality of the Mini? Is there any discernible difference as compared to a Roamio? I think if it is the same I might as well go with the Mini since it's cheaper both in equipment prices and in ongoing Comcast cablecard charges.