I have been there and back with L lenses and finally the other day I got the nifty-fifty for the first time and all I can say is WOW!
That little plastic thing can rock with the 1Ds III and some know how.
I used it at a pool party last night to get some all around photos with some fill flash and I was very pleased with the sharpness, even when cropping and zooming.
Albeit, it isn't an 85L (my only beloved L), but when you are around the pool, you don't get the L glass out, if you can help it (at least I don't).
Oh, don't give me a bunch of jazz about not getting the L out, but using a 1ds III around the pool. I know, I know...