When you start crossing the 250 to 400 watt range, all the connections/adapters/plugs you need to run CFLs make them not as "Cost" efficient. A lot of people still use them probably up to 400 watts or more, just b/c they can add a few CFL every week or so and "Amortize" the cost of the lighting. Heat/ventilation also makes CFL a better choice over MH/HPS at the 250 to 400W range. As for the 42W bulbs vs. the 23 to 25W bulbs, I just priced online and in Big Box stores, and you can get about 100W of CFL with four X 25W bulb for $10 to $12. Since 42W bulbs are b/t $10 to $13 each, you are getting almost 2.5 times the wattage for the same cost with the 25Watters. But like I said earlier, the fittings/connecters/plugs start getting annoying/expensive with CFL. All in all, it probably balances out with the 25 and 42W bulbs, if you figure in extra plugs/cords/fixtures needed for the 25W bulbs.
If you want 250 to 400W of light instantly, go HPS/MH. If you do not mind all the extra hassle of CFL lights, then that works as well. Finally, what I think happens a lot with personal growers, is they can start with just 50 to 100W of CFL to get plants vegged up to maybe 3 to 4 weeks (talking only 1 or 2 plants). Then they can either keep going with CFL, or then have 3 to 4 weeks of research/thinking time to decide if MH/HPS is the better choice for flowering and future grows.
Just a little 2 cents for thought.