Well for flowering stage you should go to home depot, they have the giant cfls(2700k) that are 68watts 300 eqivalent and give out about 4200 lumens and are about 16 bucks each.. good deal if u ask me.
i just bought a box of 6 26w ge cfl's today for around $12 at walmart
with y splitters and 2 boxes of 26w, you'll get more lumens than 6 42w
and the 6 42w will cost you about $50 minimum
One 42 watt bulb has given a noticable difference over 2x 26 watts on a few plants in my grow room. 42 watts give a much larger margin of distance between the plant allowing it to grow without losing lumens. You are somewhat right though. A very close 42 watt compared to 2 very close 26 watts... the 26 watts would output more "Lux".