My definition of 'razor sharp' is anything that outresolves the 5D2 sensor, at least in the centre at f/4-5.6, at PZ's 3700 mark.
Like the TS-E 24, 24/1.4L, the Samyang 35, the 14/2.8LII, the 85/1.2LII (almost).
I'm happy putting the 40mm Pancake in the same basket as those ones, and it's even cheaper than the Samyang and has AF too.