Out of 75% temo (100-200 distance or 300 distance) and 2x500 (atleast 20 minutes rest), which would benefit 200/400 fitness most, regarding cardiovacular system (CO and capillarisation), lactic tolerance, and energy pathways.
The 500s are more fatiguing, but the tempo sessions are of greater overall distance and therefore fatigue metabolite (inc lactic), capillary stimulation, CO, and energy pathways (although differences in recruitment) are for longer duration although of decreased magnitude. The exceptions would be CO which can reach the same levels during tempo, and blood lacic which may even exceed the levels of the 500 session.