I'm not sure if the 1.4 is sharper wide open. Although the 50mm f/1.4 at the 2.0 aperture is similar to the 50mm f/1.8 at 1.8 aperture in sharpness.
My 1.4 open at 1.4 looks very soft, but it's a great additional stop. Here's a video where I shot wide open under incredibly dark lighting conditions (trust me, the camera see's better than my naked eye on this vid)
Okay lets play a game...what about a 1.8 v 1.4 v 1.2? I know they're all different price ranges, but I'm looking to just buy one lens and stick with it for a while, while I refill my pockets from buying that D90
Well open at 1.4, it was just a dark 60 watt light bulb from the ceiling and just the PSP [see the pink/purple light reflecting off her face] and that's all that's needed to light that scene.
I'd think a brighter light bulb, probably a 100 watt would be needed to do the same thing with the 1.8 lens.
Wow man, you girl is looking great under that 60W (all due respect, of course!). I liked your first post with the D90 as well, you're getting good in finding some pretty nice lighting conditions under overhead practicals!
And yes, you have a point. The more sensitive your camera+lens is, more opportunities of shots like those appear.