I watched the final stage of the TdF tonight and the last 8 laps (32 miles) on the Champs-Élysées looked fast especially the last 20 minutes. I searched but could not find an actual recorded average speed. I would estimate the speed over 32 mph even with the climbing section up the Champs-Élysées. On the downhill section, the commentators were constantly saying the speed was 40 mph.
I would find it difficult to imagine a faster average road race speed than the UCI world tour riders racing loops in Paris setting up for a sprint finish for the final stage win for the TdF.