When taking the geometric mean of all the performance benchmarks carried out, the combination of one Zen 4 and one Zen 4C core was around 84% the speed of two Zen 4 cores – not bad at all for the Zen 4C showing especially with it topping out at 3.7GHz rather than 5.0GHz.
the geometric mean showed 1x Z4 was 3.597, 1x Z4 + 1x Z4C was 5.427, and 2x Z4 was 6.481
so the Z4C core added 1.83 compared to the 2nd Z4 which added 2.884, so a Z4C core is about 63% as fast as a Z4 core with 74% of the clockspeed