for max effecincy of not wasting kits, 3 common items or 1 rare item equals one level 5 common kit
for a rare level 17 kit you could use 2 maxed common kits and 1 level 5 common kit
maxing a non E-M legendary item is 4 kits, L-M is 5 (max rare kits)
maxing a E-M myth from level 1-50 is 525k boost power so 10 max rare kits, and a level 16 rare kit