It is exactly the same, if both motors differs only in KV, then loses in iron are also the same, and since internal resistance changes with power of 2 then also loses in copper are the same.
for example if you have motor with kv=1000 on 10 turns of winding, running with 4 cells at 20A and Ir=0.1 then loses in copper are 20^2 * 0.1 = 40W
if you go to motor with kv =500, it will need 20 turns, what leads to Ir= 0.4 and current 10A on 8 cells (makes the same input power) and loses in copper are 10^2 * 0.4 what is the same 40W
The difference can be in ESC, but if you need ESC for higher voltage, it will have also higher Ir and also switching loses will be aproximately the same.
The key tis to use proper number of cells to keep proper head room in foltage for keeping rpm loaded and with discharged battery at as much as possible "open choke"