I decided to take four pictures of my room lit by my F40T12 strip light, lit by each combination of 40 and 34 watt lamps, and residential grade and full power ballasts. Components used were my GE Mainlighter F40CW, my GE F34CW/C41/ECO, my Philips RL-140-TPC, and my Advance R-140-1-TP. The results are quite interesting.

Unsurprisingly, the 40 watt lamp puts out noticeably more light than the 34 watt lamp, on both ballasts. Also, the 40 watt lamp puts out noticeably more light on the full power ballast than it does on the residential grade ballast. Interestingly, though, the 34 watt lamp isn't that much brighter on the full power ballast than it is on the residential grade ballast! There is a difference in the photos, but it's very small. So when one is restricted to using 34 watt lamps, it might be more economical to run them on a residential-grade ballast! With 40 watt lamps, it just depends on how much light you want.

Sometime I'll make a video slideshow of the photos, just to make it easier to directly compare them.