DxO tested the Sony A7c performance and unsurprisingly the results are about the same as the one of the A7III:
Featuring a rangefinder-style body, the Sony A7C is an intriguing step between the Sony A6xxx series and the DSLR-style A7xxx models. While targeting the hybrid stills and video market, the design means it’s likely to find favor with vloggers and others looking for a highly compact and portable full-frame camera, and it’s an attractive alternative to the larger A7 III and A9 models. At launch, the price is advantageous as well.
The BSI-CMOS in the Sony A7C performs well altogether. The results are practically identical to the sensors in the Sony A7 III and A9 II, and it produces a nice balance between maximum dynamic range at low ISOs and maintaining a usefully wide dynamic range at higher ISO settings. And the same can be said for color depth. All combined, the Sony A7C is an attractive option for landscape, travel, wedding, and portrait photographers, while the rangefinder-style body should also appeal to the traditional street photographer.