this is kinda hard to explain, lets start with Bulb color Temp.
When a bulb says 5000K or 6500k that is simply referring to its peak color temp. many/most bulbs emit light at many different temps all at the same time, some have numerous peaks slightly lower than the rated one at other color temps. generally the highest peak represents how we see the light given off by it. to get an accurate idea of the % color temps of a bulb you need to see the spectrum graph for the bulb.
now lets talk lumins, this is the amount of light put off by the bulb. now take 2 graphs of bulb color temps, lets say a 1000watt MH 5500k bulb and a 23 watt 6500k CFL. the 1000w MH produces about 130,000 lumins and the 23 watt CFL about 1800. So the HM produces nearly 75 time the light the CFL does.
now remember those graphs we looked up of color temps of different bulbs and how they show the light ranges in percent output. when shown as % output the 6500K CFL appears to line up very well with the light that can be absorbed by a plant for photosynthesis and the 5500k HM seems to line up ok but not as well as the CFL. now heres the kicker, to see how well each one preforms in reality, imagine laying all 3 graphs on top of each other and seeing how much of the absorption graph each of the light spectrum graphs cover up. Still looks like the CFL is coming out on top right (woot cheap light out preform the expensive ones!!!, except there is one more thing) now take the CFL light output graph and divide its output at all temps by 75, now there is only a tiny little line at the bottom of the graph that represents the actual usable light produced by the 23 watt CFL (using the 1000watt MH as the standard).
i hope by explanation makes since with out pics. also 1100 and 1800 lumins is pretty insignificant in reality and would produce a nearly unnoticeable difference IMO, but if your talking 1100 and 130000 thats a different story. also penetrating (the amount the light degrades over a distance) is important to factor in if you are veging larger plants.